The Project Gutenberg eBook, Maxims and Instructions for the Boiler Room, by N. (Nehemiah) Hawkins

MAXIMS

AND

INSTRUCTIONS

FOR

THE BOILER ROOM.

RICHARD TREVITHICK.

Maxims and Instructions

FOR

The Boiler Room.

USEFUL TO

Engineers, Firemen & Mechanics,

RELATING TO STEAM GENERATORS, PUMPS, APPLIANCES, STEAM HEATING, PRACTICAL PLUMBING, ETC.

By N. HAWKINS, M. E.,

Honorary Member National Association of Stationary Engineers, Editorial Writer, Author of Hand Book of Calculations for Engineers and Firemen, Etc., Etc.

Comprising Instructions and Suggestions on the Construction, Setting, Control and Management of Various Forms of Steam Boilers; on the Theory and Practical Operation of the Steam Pump; Steam Heating; Practical Plumbing; also Rules for the Safety Valve, Strength of Boilers, Capacity of Pumps, Etc.

THEO. AUDEL & CO., Publishers,
63 FIFTH AVE., Cor. 13th St.,
New York.

Copyrighted
1897—1898—1903
by
Theo, Audel & Co.

PREFACE.

CONTENTS.

OLIVER EVANS.GEORGE STEPHENSON.ROBERT FULTON.

INTRODUCTION.

Each successive generation of engineers has added certain unwritten experiences to the general stock of knowledge relating to steam production, which have been communicated to their successors, and by them added to, in their turn; it is within the province of this book to put in form for reference, these unwritten laws of conduct, which have passed into Maxims among engineers and firemen—a maxim being an undisputed truth, expressed in the shortest terms.

These are the questioning thoughts which fill, while on duty, more or less vividly, the minds of both engineers and firemen, and it is the purpose of this volume to answer the enquiries, as far as may be without attempting too much; for the perfect knowledge of the operations carried on within the boiler-room involves an acquaintance with many branches of science. In matters relating to steam engineering, it must be remembered that “art is long and time is short.”

The utility of such a book as this is intended to be, no one will question, and he who would not be a “hewer of wood and a drawer of water” to the more intelligent and well-informed mechanic, must possess to a considerable extent the principles and rules embraced in this book; and more especially, if he would be master of his profession and reputed as one whose skill and decisions can be implicitly relied upon.

The author in the preparation of the work has had two objects constantly in view; first to cause the student to become familiarly acquainted with the leading principles of his profession as they are mentioned, and secondly, to furnish him with as much advice and information as possible within the reasonable limits of the work.

While it is a fact that some of the matter contained in this work is very simple, and all of it intended to be very plain, it yet remains true that the most expert living engineer was at one time ignorant of the least of the facts and principlesxi here given, and at no time in his active career can he ever get beyond the necessity of knowing the primary steps by which he first achieved his success.

The following taken from the editorial columns of the leading mechanical journal of the country contains the same suggestive ideas already indicated in the “soliloquy of an engineer:”

The old meaning of the word lever was “a lifter” and this book is intended to be to its attentive student, a real lever to advance him in his life work; it is also to be used like a ladder, which is to be ascended step by step, the lower rounds of which, are as important as the highest.

It is moreover, the earnest wish of the editor that when some, perchance may have “climbed up” by the means of this, his work, they may in their turn serve as lifters to advance others, and by that means the benefits of the work widely extended.

MATERIALS.

The things with which the engineer has to deal in that place where steam is to be produced as an industrial agent, are

1. The Steam Generator.

2. Air.

3. Fuel.

4. Water.

5. Steam Appliances.

Starting with these points which form a part of every steam plant, however limited, however vast, the subject can easily be enlarged until it embraces a thousand varied divisions extending through all time and into every portion of the civilized world.

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It is within the scope of this work to so present the subjects specified, that the student may classify and arrange the matter into truly scientific order.

MATERIALS.

In entering the steam department, where he is to be employed, the eye of the beginner is greeted with the sight of coal, water, oil, etc., and he is told of invisible materials, such as air, steam and gases; it is the proper manipulation of these seen and unseen material products as well as the machines, that is to become his life task. In aiding to the proper accomplishment of the yet untried problems nothing can be more useful than to know something of the nature and history of the different forms of matter entering into the business of steam production. Let us begin with

Coal.

The source of all the power in the steam engine is stored up in coal in the form of heat.

And this heat becomes effective by burning it, that is, by its combustion.

Coal consists of carbon, hydrogen, nitrogen, sulphur, oxygen and ash. These elements exist in all coals but in varying quantities.

These are the common proportions of the best sorts:

In burning coal or other fuel atmospheric air must be introduced before it will burn; the air furnishes the oxygen, without which combustion cannot take place.

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It is found that in burning one lb. of coal one hundred and fifty cubic feet of air must be used and in every day practice it is necessary to supply twice as much; this is supplied to the coal partly through the grate bars, partly through the perforated doors, and the different devices for applying it already heated to the furnace.

WOOD.

Wood as a combustible, is divisible into two classes: 1st, the hard, compact and comparatively heavy, such as oak, ash, beech, elm. 2d, the light colored soft, and comparatively light woods as pine, birch, poplar.

Wood when cut down contains nearly half moisture and when kept in a dry place, for several years even, retains from 15 to 20 per cent. of it.

The steam producing power of wood by tests has been found to be but little over half that of coal and the more water in it the less its heating power. In order to obtain the most heating power from wood it is the practice in some works in Europe where fuel is costly, to dry the wood fuel thoroughly, even using stoves for the purpose, before using it. This “hint” may serve a good purpose on occasion.

The composition of wood reduced to its elementary condition will be found in the table with coal.

PEAT.

Peat is the organic matter or vegetable soil of bogs, swamps and marshes—decayed mosses, coarse grasses, etc. The peat next the surface, less advanced in decomposition, is light, spongy and fibrous, of a yellow or light reddish-brown color; lower down it is more compact, of a darker-brown color, and in the lowest strata it is of a blackish brown, or almost a black color, of a pitchy or unctuous feel.

Peat in its natural condition generally contains from 75 to 80 per cent. of water. It sometimes amounts to 85 or 90 per cent. in which case the peat is of the consistency of mire.

When wet peat is milled or ground so that the fibre is broken, crushed or cut, the contraction in drying is much15 increased by this treatment; and the peat becomes denser, and is better consolidated than when it is dried as it is cut from the bog; peat so prepared is known as condensed peat, and the degree of condensation varies according to the natural heaviness of the peat. So effectively is peat consolidated and condensed by the simple process of breaking the fibres whilst wet, that no merely mechanical force of compression is equal to it.

In the table the elements of peat are presented in two conditions. One perfectly dried into a powder before analyzing and the other with 25 per cent. of moisture.

The value of peat as a fuel of the future is an interesting problem in view of the numerous inroads made upon our great natural coal fields.

TAN.

Tan, or oak bark, after having been used in the process of tanning is burned as fuel. The spent tan consists of the fibrous portion of the bark. Five parts of oak bark produce four parts of dry tan.

STRAW.

COKE, CHARCOAL, PEAT CHARCOAL.

These are similar substances produced by like processes from coal, wood, and peat and they vary in their steam-producing power according to the power of the fuels from which they are produced. The method by which they are made is termed carbonization, which means that all the gases are removed by heat in closed vessels or heaps, leaving only the carbon and the more solid parts like ashes.

LIQUID AND GAS FUELS.

Under this head come petroleum and coal gas, which are obtained in great variety and varying value from coal and coal oil. The heating power of these fuels stands in the front rank, as will be seen by the table annexed.

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There are kinds of fuel other than coal, such as wood, coke, sawdust, tan bark, peat and petroleum oil and the refuse from oil. These are all burned with atmospheric air of which the oxygen combines with the combustible part of the fuel while the nitrogen passes off into the chimney as waste.

The combustible parts of coal are carbon, hydrogen and sulphur and the unburnable parts are nitrogen, water and the incombustible solid matters such as ashes and cinder. In the operation of firing under a boiler the three first elements are totally consumed and form heat; the nitrogen, and water in the form of steam, escapes to the flue, and the ashes and cinders fall under the grates.

The anthracite coal retain their shape while burning, though if too rapidly heated they fall to pieces. The flame is generally short, of a blue color. The coal is ignited with difficulty; it yields an intense local or concentrated heat; and the combustion generally becomes extinct while yet a considerable quantity of the fuel remains on the grate.

The dry or free burning bituminous coals are rather lighter than the anthracites, and they soon and easily arrive at the burning temperature. They swell considerably in coking, and thus is facilitated the access of air and the rapid and complete combustion of their fixed carbon.

The method of firing with different sorts of fuel will be treated elsewhere.

AIR.

The engineer’s success in the management of the furnace depends quite as much upon his handling the air in the right mixtures and proportions as it does in his using the fuel—for

1. Although invisible to the eye air is as much a material substance as coal or stone. If there were an opening into the interior of the earth which would permit the air to descend its density would increase in the same manner at it diminishes in the opposite direction. At the depth of about 34 miles it would be as dense as water, and at the depth of 48 miles it would be as dense as quicksilver, and at the depth of about 50 miles as dense as gold.

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2. Air is not only a substance, but an impenetrable body; as for example: if we make a hollow cylinder, smooth and closed at the bottom, and put a stopper or solid piston to it, no force will enable us to bring it into contact with the bottom of the cylinder, unless we permit the air within it to escape.

3. Air is a fluid which is proved by the great movability of its parts, flowing in all directions in great hurricanes and in gentle breezes; and also by the fact that a pressure or blow is propagated through all parts and affects all parts alike.

4. It is also an elastic fluid, thus when an inflated bladder is compressed it immediately restores itself to its former situation; indeed, since air when compressed restores itself or tends to restore itself, with the same force as that with which it is compressed, it is a perfectly elastic body.

5. The weight of a column of air one square foot at the bottom is found to be 2156 lbs. or very nearly 15 lbs. to the square inch, hence it is common to state the pressure of the atmosphere as equal to 15 lbs. to the square inch.

It follows from these five points that the engineer must consider air as a positive, although unseen, factor with which his work is to be accomplished.

What air is composed of is a very important item of knowledge. It is made of a mixture of two invisible gases whose minute and inconceivably small atoms are mingled together like a parcel of marbles and bullets—that is while together they do not lose any of their distinctive qualities. The two gases are called nitrogen and oxygen, and of 100 parts or volumes of air 79 parts are of nitrogen and 21 parts of oxygen; but by weight (for the oxygen is the heaviest) 77 of nitrogen and 23 of oxygen.

The oxygen is the part that furnishes the heat by uniting with the coal—indeed without it the process of combustion would be impossible: of the two gases the oxygen is burned in the furnace, more or less imperfectly, and the nitrogen is wasted.

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Table of Evaporation.

In order to arrive at the money value of the various fuels heretofore described a method of composition has been arrived at which gives very accurately their comparative worth. The rule is too advanced for this elementary work, but the following results are plainly to be understood, and will be found to be of value.

The way to read this table is as follows: “one lb. coal has an average evaporative capacity of 14.62 lbs. of water,” or

One lb. of peat with one-quarter moisture will evaporate, if all the heat is utilized 7.41 lbs. of water.

In practice but little over half of these results are attained, but for a matter of comparison of the value of one kind of fuel with another the figures are of great value; a boiler burning wood or tan needs to be much larger than one burning petroleum oil.

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FIRE IRONS.

The making or production of steam requires the handling of the fuel, more or less, until its destruction is complete, leaving nothing behind in the boiler room, except ashes and clinkers. The principal tools used by the attendant, to do the task most efficiently are: 1. The scoop shovel. 2. The poker. 3. The slice bar. 4. The barrow.

Fig. 1.

Fig. 1. represents the regular scoop shovel commonly called “a coal shovel,” but among railroad men and others, known as a locomotive or charging scoop. The cut also represents a regular shovel. Both these are necessary for the ordinary business of the boiler room.

Fig. 2.

In cut 2 are represented a furnace poker, A, and two forms of the slice bar. They are all made by blacksmiths from round iron, some 7 or 8 feet long and only vary in the form of the end. The regular slice bar is shown in C, Fig. 2; and “the dart” a special form used largely on locomotives is shown in B.

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The dexterous use of these important implements can merely be indicated in print, as it is part of the trade which is imparted by oral instruction. One “point” in making the slice bar may be mentioned to advantage—the lower side should be perfectly flat so that it may slide on the surface of the grate bars as it is forced beneath the fire—and the upper portion of the edge should be in the shape of a half wedge, so as to crowd upwards the ashes and clinkers while the lower portion slides along.

There is sometimes used in connection with these tools an appliance called a Lazy Bar. This is very useful for the fireman when cleaning a bituminous or other coal fire: it saves both time and fuel as well as steam. It is a hook shaped iron, ingeniously attached above the furnace door, so that it supports the principal part of the weight of the heavy slice bar or poker when being used in cleaning out the fires.

Fig. 3.

Equally necessary to the work of the boiler-room is the barrow shown in cut. There are many styles of the vehicle denominated respectively—the railroad barrow, the ore and stone barrow, the dirt barrow, etc.; but the one represented in fig. 3 is the regular coal barrow.

In conveying coal to “batteries” of boilers, in gas houses and other suitable situations the portable car and iron track are nearly always used instead of the barrow. In feeding furnaces with saw dust and shavings large iron screw conveyors are frequently employed, as well as blowers—In the handling of the immense quantities of fuel required, the real ingenuity of the engineer in charge has ample opportunity for exercise.

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There are also used in nearly all boiler rooms HOES made of heavy plate iron, with handles similar to those shown in the cuts representing the slice bar and poker. A set of two to four hoes of various sizes is a very convenient addition to the list of fire tools; a light garden hoe for handling ashes is not to be omitted as a labor saving tool.

HANDY TOOLS.

Besides the foregoing devices for conducting the preliminary process of the steam generation, the attendant should have close at hand a servicable HAND HAMMER, a SLEDGE for breaking coal and similar work, and A SCREW WRENCH and also a light LADDER for use about the boiler and shafting.

In addition to these there are various other things almost essential for the proper doing of the work of the boiler room,—Fire and Water Pails, Lanterns, Rubber Hose, etc., which every wise steam user will provide of the best quality and which the engineer will as carefully keep in their appointed places ready for instant service.

Fig. 4.

To these familiar tools can be added FILES, LACE CUTTERS, BOILER-FLUE BRUSHES, STOCK and DIES, PIPE-TONGS, SCREW JACKS, VISES, etc., all of which when used with skill and upon right occasion pay a large return on their cost.

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THE TOOL BOX.

The complex operations of the boiler room, its emergencies and varying conditions demand the use of many implements which might at first thought be out of place. The following illustrations exhibit some of these conveniences.

Fig. 5.

Fig. 5, letter A, show the common form of COMPASSES which are made from 3 to 8 inches long. Letter B, illustrates the common steel compass dividers, which are made from 5 to 24 inches in length.

Fig. 6.

In this illustration, A exhibits double, inside and outside Calipers; B, adjustable outside Calipers; C, inside; and D outside, plain calipers.

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THE FIRING OF STEAM BOILERS.

The care and management of a steam boiler comprises three things:

1. The preparation, which includes the partial filling with water and the kindling of the fire.

2. The running, embracing the feeding, firing and extinction or banking of the fire.

3. The cleaning out after it has been worked for some time.

To do this to the best advantage, alike to owner and employee, can be learned only by practice under the tuition of an experienced person. The “trick” or unwritten science of the duties of the skillful fireman must be communicated to the beginner, by already experienced engineers or firemen or from experts who have made the matter a special study. Let it be understood that the art of firing cannot be self taught.

The importance of this knowledge is illustrated by a remarkable difference shown in competitive tests in Germany between trained and untrained firemen in the matter of securing a high evaporation per pound of coal. The trained men succeeded in evaporating 11 lbs. of water, as against 6.89 lbs. which was the best that the untrained men could obtain.

It is certain that a poor fireman is a dear man at any price, and that a competent one may be cheap at twice the wages now paid. Suppose, for instance, a man who burns three tons a day is paid $2.00 for such service, and that in so doing he is wasting as little as 10 per cent. If the coal cost $4.50 per ton the loss will be $1.35 per day, or what is equivalent to paying a man $3.35 per day who can save this amount.

The late Chief Engineer of Philadelphia Water Works effected an annual saving to the city of something like $50,000; and recently the weekly consumption of a well established woolen mill was reduced from 71 to 49 tons, a clear saving of 22 tons by careful attention to this point.

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It is apparent that any rules or directions which might be given for one system would not apply equally to other forms of boilers and this may be the principal reason that the art is one so largely of personal instruction. Some rules and hints will, however, be given to the beginner, which may prove of advantage in fitting the fireman for an advanced position; or to assure him permanence in his present one.

No two boilers alike. It is said that no two boilers, even though they seemed to be exactly alike—absolute duplicates—ever did the same, or equal service. Every steam boiler, like every steam engine, has an individuality of its own, with which the person in charge has to become acquainted, in order to obtain the best results from it.

The unlikeness in the required care of steam engines which seem to be exactly the same, is still more marked in the different skill and experience demanded in handling locomotive, marine, stationary, portable boilers and other forms of steam generators.

Before Lighting the Fire under the boiler in the morning, the engineer or fireman should make a rapid yet diligent examination of various things, viz.: 1. He should make sure that the boiler has the right quantity of water in it—that it has not run out during the night or been tampered with by some outside party; very many boilers have been ruined by neglecting this first simple precaution. 2. He should see that the safety-valve is in working order; this is done by lifting by rod or hand the valve which holds the weight upon the safety valve rod. 3. He should open the upper gauge-cock to let out the air from the boiler while the steam is forming. 4. He should examine the condition of the grate-bars and see that no clinkers and but few ashes are left from last night’s firing. 5. And finally, after seeing that everything is in good shape, proceed to build the fire as follows:

On Lighting the Fire. When quite certain that everything is in good condition, put a good armful of shavings or fine wood upon the grate, then upon this some larger pieces of wood to form a bed of coals, and then a little of26 the fuel that is to be used while running. Sometimes it is better to light before putting on the regular fuel, but in any case give it plenty of air. Close the fire doors, and open the ash pit, giving the chimney full draught.

When the fire is well ignited, throw in some of the regular fuel, and when this is burning add more, a little at a time, and continue until the fire is in its normal condition, taking care, however, not to let it burn too freely for fear of injury to the sheets by a too rapid heating.

It is usually more convenient to light the fire through the fire door, but where this cannot be done, a torch may be used beneath the grates, or even a light fire of shavings may be kindled in the ash pit.

At the time of lighting, all the draughts should be wide open.

As soon as the steam is seen to issue from the open upper gauge-cock it is proof that the air is out. It should now be closed and the steam gauge will soon indicate a rise in temperature.

When the steam begins to rise it should next be observed that: 1. All the cocks and valves are in working order—that they move easily. 2. That all the joints and packings are tight.

In the following two cuts are exhibited in an impressive way the difference between proper and improper firing.

Fig. 1.

Fig. 1 represents the proper mode of keeping an even depth of coal on the grate bars; the result of which will be, a uniform generation of gas throughout the charge, and a uniform temperature in the flues.

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Fig. 2.

Fig. 2 represents a very frequent method of feeding furnaces; charging the front half as high, and as near the door, as possible, leaving the bridge end comparatively bare. The result necessarily is that more air obtains access through the uncovered bars than is required, which causes imperfect combustion and consequent waste.

The duties of the fireman in the routine of the day may thus be summed up:

1st.—Begin to charge the furnace at the bridge end and keep firing to within a few inches of the dead plate.

2d.—Never allow the fire to be so low before a fresh charge is thrown in, that there shall not be at least three to five inches deep of clean, incandescent fuel on the bars, and equally spread over the whole.

3d.—Keep the bars constantly and equally covered, particularly at the sides and the bridge end, where the fuel burns away most rapidly.

4th.—If the fuel burns unequally or into holes, it must be leveled, and the vacant spaces must be filled.

5th.—The large coals must be broken into pieces not bigger than a man’s fist.

6th.—When the ash pit is shallow, it must be the more frequently cleared out. A body of hot cinders, beneath them, overheats and burns the bars.

7th.—The fire must not be hurried too much, but should be left to increase in intensity gradually. When fired properly the fuel is consumed in the best possible way, no more being burned than is needed for producing a sufficient quantity of steam and keeping the steam pressure even.

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DIRECTIONS FOR FIRING WITH VARIOUS FUELS.

Firing Boilers Newly Set, etc.—Boilers newly set should be heated up very slowly indeed, and the fires should not be lighted under the boilers for at least two weeks after setting, if it is possible to wait this length of time. This two weeks enables all parts of the mason work to set gradually and harden naturally; the walls will be much more likely to remain perfect than when fires are lighted while the mortar is yet green.

When fire is started under a new boiler the first time, it should be a very small one, and no attempt should be made to do more than moderately warm all parts of the brick work. A slow fire should be kept up for twenty-four hours, and on the second day it may be slightly increased. Three full days should elapse before the boiler is allowed to make any steam at all.

When the pressure rises, it should not be allowed to go above four or five pounds, and the safety valve weight should be taken off to prevent any possibility of an increase. Steam should be allowed to go through all the pipes attached for steam, and blow through the engine before any attempt is made to get pressure on them. The object of all these precautions and this care is to prevent injury by sudden expansion, which may cause great damage.

Firing with Coke.

Coke, in order to be completely consumed, needs a greater volume of air per pound of fuel than coal. Theoretically it needs from 9 to 10 lbs. of air to burn a pound of coal, and 12 to 13 lbs. of air to burn a pound of coke.

Coke, therefore, requires a more energetic draft, which is increased by the fact that it can only burn economically in a thick bed. It is also necessary to take into account the size of the pieces.

The ratio between the heating and grate surface should be less with coke than with coal; that is to say, the grate should be larger.

The difference amounts to about 33 per cent. In fact,29 about 9³⁄₄ lbs. of coke should be burned per hour on each square foot of grate area, while at least 14¹⁄₂ lbs. of coal can be burned upon the same space.

The high initial temperature which is developed by the combustion of coke requires conducting walls. Therefore the furnace should not be entirely surrounded by masonry; and the plates of the boiler should form at least the crown of the fire-box. In externally fired boilers, the furnace should be located beneath and not in front of the boiler. Internal fire-boxes may be used, but the greatest care should be exercised to avoid any incrustation of the plates, and in order that this may be done, only the simplest forms of boilers should be used. With coke it is not essential that long passages should be provided for the passage of the products of combustion, since the greater part of the heat developed is transmitted to the sheets in the neighborhood of the furnace.

Since coke contains very little hydrogen, the quick flaming combustion which characterizes coal is not produced, but the fire is more even and regular. And, finally, the combustion of coal is distinguished by the fact that in the earlier phases there is usually an insufficiency of air, while in the last there is no excess.

The advantage of coke over raw soft coal as a fuel is that otherwise useless slack can be made available by admixture in its manufacture, and especially that it can be perfectly and smokelessly burnt without the need of skilled labor. And we cannot doubt that the public demand for a clear and healthy atmosphere will finally result in the almost complete substitution of coke fuel for soft lump coal.

Sixteen Steam Boilers in a large mill in Massachusetts of 54 and 60 inches in diameter are fired as follows:

There are three separate batteries; one of five boilers, one of eight and one of three. Each boiler is fired every five minutes. There are two firemen for the battery of twelve and30 one for each of the others. A gong in each fire-room is operated by electricity in connection with a clock. The duty of the fireman is this, that when the gong strikes he commences at one end of his fire-room and fires as rapidly as possible, opening one-half of each furnace door. The coal is thrown only on one-half of the grate space as he rapidly fires each boiler, the other half is covered at the next sounding of the gong. The old style of straight grate is used. The fires are kept six inches thick or a little thicker. No slicing is done. It is, of course, to be understood that the firemen arrange the quantity of coal fired according to the apparent necessity of the case. Bituminous coal is used, and it is broken into small pieces, so as to distribute well. Accurate account is kept of the quantity of coal used and the engines are frequently indicated.

Twenty Horse Power.—An old engineer says the way he handled his boiler of this size, burning 800 lbs. of screenings per day, is as follows:

My method is to run as heavy a fire as my fire-box will allow to be kept under the bridge wall, and not to disturb it more than once in a ten-hours run, then clean out with care and as speedily as possible, dress light and let it come up and get ready to bank. In banking I make sure to have an even fire, as deep as the bridge wall will allow. Then I shut my dampers and let it lie. In the morning I open and govern by the dampers. I do not touch my fire until 3.30 or 4 o’clock in the afternoon, and then proceed to clean as before.

Firing with Coal Tar.—The question of firing retort benches with tar instead of coke has engaged the attention of gas managers for many years, and various modes have been adopted for its management. The chief difficulty has been in getting a constant flow of tar into the furnace, uninterrupted by stoppages caused by the regulating cock or other appliance not answering its purpose and by the carbonizing of the tar in the delivery pipe, thus choking it up and rendering it uncertain in action. To obviate these31 difficulties various plans have been resorted to, but the best means for overcoming them are thus described; fix the tar supply tank as near the furnace to be supplied as convenient, and one foot higher than the tar-injector inlet. A cock is screwed into the side of the tank, to which is attached a piece of composition pipe ³⁄₈-inch in diameter, ten inches long. To this a ¹⁄₂-inch iron service pipe is connected, the other end of which is joined to the injector. By these means it is found that at the ordinary temperature of the tar well (cold weather excepted) four gallons of tar per hour are delivered in a constant steam into the furnace. If more tar is required, the piece of ³⁄₈-inch tube must be shortened, or a larger tube substituted, and if less tar is required it must be lengthened. The risk of stoppage in the nozzle of the injector is overcome by the steam jet, which scatters the tar into spray and thus keeps everything clear. Trouble being occasioned by the retorts becoming too hot, in which case, on shutting off the flow of tar for a while, the tar in the pipe carbonized and caused a stoppage, a removable plug injector is fitted and ground in like the plug of a cock, having inlets on either side for tar and steam. This plug injector can be removed, the tar stopped in two seconds and refixed in a similar time. The shell of the injector is firmly bolted to the top part of the door frame. The door is swung horizontally, having a rack in the form of a quadrant, by which it is regulated to any required height, and to admit any quantity of air.

Firing with Straw.—The operation of burning straw under a boiler consists in the fuel being fed into the furnace only as fast as needed. When the straw is handled right, it makes a beautiful and very hot flame and no smoke is seen coming from the stack. The whole secret of getting the best results from this fuel is to feed it into the furnace in a gradual stream as fast as consumed. When this is done complete combustion is the result. A little hole maybe drilled in the smoke-box door, so that the color of the fire can be seen and fire is handled accordingly. When the smoke comes from the stack the color of the flame is that of a good gas jet. By feeding a32 little faster the color becomes darker and a little smoke comes from the stack; feeding a little faster the flame gets quite dark and the smoke blacker; faster still, the flame is extinguished, clouds of black smoke come from the stack, and the pressure is falling rapidly.

Firing with Oil.—Great interest is now manifested in the use of oil as fuel. There are various devices used for this purpose, most of them depending upon a steam jet to atomize the oil, or a system of retorts to first heat the oil and convert it into gas, before being burned.

Another method in successful operation is the use of compressed air for atomizing the oil—air being the element nature provides for the complete combustion of all matter. The cleanliness of the latter system and its comparative freedom from any odor of oil or gas and its perfect combustion, all recommend it. Among the advantages claimed for the use of oil over coal are 1, uniform heat; 2, constant pressure of steam; 3, no ashes, clinkers, soot or smoke, and consequently clean flues; 4, uniform distribution of heat and therefore less strain upon the plates.

Firing on an Ocean Steamer like the “Umbria.”—The men come on in gangs of eighteen stokers or firemen and twelve coal passers, and the “watch” lasts four hours. The “Umbria” has 72 furnaces, which require nearly 350 tons of coal a day, at a cost of almost $20,000 per voyage. One hundred and four men are employed to man the furnaces, and they have enough to do. They include the chief engineer, his three assistants, and ninety stokers and coal passers.

The stoker comes to work wearing only a thin undershirt, light trousers and wooden shoes. On the “Umbria” each stoker tends four furnaces. He first rakes open the furnaces, tosses in the coal, and then cleans the fire; that is, pries the coal apart with a heavy iron bar, in order that the fire may burn freely. He rushes from one furnace to another, spending perhaps two or three minutes at each. Then he dashes to the air pipe, takes his turn at cooling off, and waits for another33 call to his furnace, which comes speedily. When the “watch” is over, the men schuffle off, dripping with sweat from head to foot, through long, cold galleries to the forecastle, where they turn in for eight hours. Four hours of scorching and eight hours sleep make up the routine of a fireman’s life on a voyage.

The temperature is ordinarily 120°, but sometimes reaches 160°; and the work is then terribly hard. The space between the furnaces is so narrow that when the men throw in coal they must take care when they swing back their shovels, lest they throw their arms on the furnace back of them.

In a recent trial of a government steamer the men worked willingly in a temperature of 175°, which, however, rose to 212° or the heat of boiling water. The shifts of four hours were reduced to 2 hours each, but after sixteen men had been prostrated, the whole force of thirty-six men refused to submit to the heat any longer and the trial was abandoned.

There is no place on ocean or land where more suffering is inflicted and endured by human beings than in these h——holes, quite properly so called; it is to be hoped that the efforts towards reform in the matter will not cease until completely successful.

Firing of Sawdust and Shavings.—“The air was forced into the furnace with the planer shavings at a velocity of about 12 feet per second, and at an average temperature of about 60 degrees Fahrenheit. The shavings were forced through a pipe 12 inches in diameter, above grate, into the combustion chamber. The pipe had a blast gate to regulate the air in order to maintain a pressure in the furnace, which a little more than balanced the ascending gases in the funnel or chimney. All the fireman had to do was to keep the furnace doors closed and watch the water in the gauges of his boiler. The combustion in the furnace was complete, as no smoke was visible. The shavings were forced into the combustion chamber in a spray-like manner, and were caught into a blaze the moment they entered. The oxygen of the air so forced into the furnace along with the shavings gave full support to the combustion.34 The amount of shavings consumed by being thus forced into the furnace was about fifty per cent. less than the amount consumed when the fireman had to throw them in with his shovel.”

Fig. 9.

It is an important “point” when burning shavings or sawdust with a blast, to keep the blower going without cessation, as there have been disastrous accidents caused by the flames going up the shutes, thence through the small dust tubes leading from the bin to the various machines.

Fig. 10.

In firing “shavings” by hand it is necessary to burn them from the top as otherwise the fire and heat are only produced when all the shavings are charred. To do this, provide a half-inch gas pipe, to be used as a light poker; light the shaving fire, and when nearly burned take the half-inch pipe and divide the burning shavings through the middle, banking them against the side-walls, as shown in Fig. 9. Now feed a pile of new shavings into the centre on the clean grate bars, as shown in Fig. 10, and close the furnace doors. The shavings will begin to burn from above, lighted from the two side fires, the air will pass through the bars into the shavings, where it will be heated and unite with the gas, making the combustion perfect, generating heat, and no smoke, and the fire will last much longer and require not half the labor in stoking.

35

FIRING A LOCOMOTIVE.

This figure exhibits the interior of the furnace of a locomotive engine, which varies greatly from the furnace of either a land or marine boiler. This difference is largely caused by the method of applying the draught for the air supply; in the locomotive this is effected by conducting the exhaust steam through pipes from the cylinders to the smoke-box and allowing it to escape up the smoke stack from apertures called exhaust nozzles; the velocity of the steam produces a vacuum, by which the products of combustion are drawn into the smoke-box with great power and forced out of the smoke stack into the open air.

To prevent the too quick passage of the gases into the flues an appliance called a fire brick arch has been adopted and has proved very efficient. In order to be self supporting it is built in the form of an arch, supported by the two sides of the fire box which serve for abutments. The arch has been sometimes replaced by a hollow riveted arrangement called a water table designed to increase the fire surface of the boiler.

36

Firing a Locomotive.—No rules can possibly be given for firing a locomotive which would not be more misleading than helpful. This is owing to the great variations which exist in the circumstances of the use of the machine, as well as the differences which exist in the various types of the locomotive.

These variations may be alluded to, but not wholly described. 1. They consist of the sorts of fuel used in different sections of the country and frequently on different ends of the same railroad; hard coal, soft coal, and wood all require different management in the furnace. 2. The speed and weight of the train, the varying number of cars and frequency of stopping places, all influence the duties of the fireman and tax his skill. 3. The temperature of the air, whether cold or warm, dry weather or rain, and night time and day time each taxes the skill of the fireman.

Hence, to be an experienced fireman in one section of the country and under certain circumstances does not warrant the assurance of success under other conditions and in another location. The subject requires constant study and operation among not only “new men” but those longest in the service.

More than in any other case to be recalled, must the fireman of a locomotive depend upon the personal instruction of the engineer in charge of the locomotive.

Firing with Tan Bark.—Tan bark can be burned upon common grates and in the ordinary furnace by a mixture of bituminous screenings. One shovel full of screenings to four or five of bark will produce a more economical result than the tan bark separate, as the coal gives body to the fire and forms a hot clinker bed upon which the bark may rest without falling through the spaces in the grate bars, and with the coal, more air can be introduced to the furnace.

The above relates to common furnaces, but special fire boxes have been recently put into operation, fed by power appliances, which work admirably. The “point” principally to be noted as to the efficacy of tan bark as a fuel, is to the effect, that like peat, the drier it is the more valuable is it as a fuel.

37

POINTS RELATING TO FIRING.

The Process of Boiling. Let it be remembered that the boiling spoken of so often is really caused by the formation of the steam particles, and that without the boiling there can be but a very slight quantity of steam produced.

While pure water boils at 212°, if it is saturated with common salt, it boils only on attaining 224°, alum boils at 220°, sal ammoniac at 236°, acetate of soda at 256°, pure nitric acid boils at 248°, and pure sulphuric acid at 620°.

On the First Application of Heat to water small bubbles soon begin to form and rise to the surface; these consist of air, which all water contains dissolved in it. When it reaches the boiling point the bubbles that rise in it are principally steam.

In the case of a new plant, or where the boiler has some time been idle it is frequently advisable to build a small fire in the base of the chimney before starting the boiler fires. This will serve to heat the chimney and drive out any moisture that may have collected in the interior and will frequently prevent the disagreeable smoking that often follows the building of a fire in the furnace.

Always bear in mind that the steam in the boilers and engines is pressing outward on the walls that confine it in every direction; and that the enormous forces you are handling, warn you to be careful.

When starting fires close the gauge cocks and safety valve as soon as steam begins to form.

Go slow. It is necessary to start all new boilers very slowly. The change from hot to cold is an immense one in its effects on the contraction and expansion of the boiler, the change of dimension by expansion is a force of the greatest magnitude and cannot be over-estimated. Leaks which start in boilers that were well made and perfectly tight can be attributed to this cause. Something must give if fires are driven on the start, and this entails trouble and expense that there is no occasion for. This custom applies to engines and steam pipes as well as to boilers. No one of any experience will open a stop valve and let a full head of live steam into a cold line of pipe or a cold engine.

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To preserve the grate bars from excessive heat, when first firing a boiler, it is well to sprinkle a thin layer of coal upon the grates before putting in the shavings and wood for starting the fire. This practice tends greatly to prolong the life of the grate-bars.

The fuel should generally be dry when used. Hard coal, however, may be dampened a little to good advantage, as it is then less liable to crowd and will burn more freely.

Air, high temperature and sufficient time are the principal points in firing a steam boiler.

In first firing up make sure that the throttle valve is closed, in order that the steam first formed may not pass over into the engine cylinder and fill it with water of condensation. If the throttle valve leak steam it should be repaired at the first opportunity.

Keep all heating surfaces free from soot and ashes.

Radiant rays go in all directions, yet they act in the most efficient manner when striking a surface exactly at a right angle to their line of movement. The sides of a fire-box are for that reason not as efficient as the surface over the fire, and a flat surface over the fire is the best that can be had, so far as that fact alone is concerned.

When combustion is completed in a furnace, then the balance of the boiler beyond the bridge wall can be utilized for taking up heat from the gases. The most of this heat has to be absorbed by actual contact; thus by the tubes the gases are finally divided, allowing that necessary contact.

Combustion should be completed on the grates for the reason that it can be effected there at the highest temperature. When this is accomplished, the fullest benefit is had from radiant heat striking the bottom of the boiler—it is just there that the bulk of the work is done.

There must necessarily be some waste of heat by its passing up the chimney to maintain draft. It is well to have the39 gases, as they enter the chimney, as much below 600 deg. F. (down to near the temperature of the steam) as you can and yet maintain perfect combustion.

Every steam engine has certain well-defined sounds in action which we call noises, for want of a better term, and it is upon them and their continuance that an engineer depends for assurance that all is going well.

This remark also applies to the steam boiler, which has, so to speak, a language of its own, varying in volume from the slight whisper which announces a leaking joint to the thunder burst which terribly follows a destructive explosion. The hoarse note of the safety-valve is none the less significant because common.

The dampers and doors to the furnace and ash-pit should always be closed after the fire has been drawn, in order to keep the heat of the boiler as long as possible.

But the damper must never be entirely closed while there is fire on the grate, as explosions dangerous in their character might occur in the furnace from the accumulated gases.

Flues or tubes should often be swept, as soot, in addition to its liability to becoming charged with a corroding acid, is a non-conductor of heat, and the short time spent in cleaning them will be repaid by the saving of labor in keeping up steam. In an establishment where they used but half a ton of bituminous coal per day, the time of raising steam in the morning was fifty per cent. longer when the tubes were unswept for one week than when they were swept three times a week.

Smoke will not be seen if combustion is perfect. Good firing will abate most of the smoke.

Coals, at the highest furnace temperature, radiate much heat, whereas gases ignited at and beyond the bridge wall radiate comparatively little heat—it is a law in nature for a solid body highly heated to radiate heat to another solid body.

Dry and Clean is the condition in which the boiler should be kept, i.e., dry outside and clean both inside and out.

40

To haul his furnace fire and open the safety valve before seeking his own safety or the preservation of property, is the duty of the fireman in the event of fire threatening to burn a whole establishment.

Many, now prominent, engineers have made their first reputation by remembering to do this at a critical time.

When Water is Pumped into the boiler or allowed to run in, some opening must be given for the escape of the contained air; usually the most convenient way is to open the upper gauge cock after the fire has been lighted until cloudy steam begins to escape.

In a summary of experiments made in England, it is stated that:—

“A moderately thick and hot fire with rapid draft uniformly gave the best results.

“Combustion of black smoke by additional air was a loss.

“In all experiments the highest result was always obtained when all the air was introduced through the fire bars.

“Difference in mode of firing only may produce a difference of 13 per cent. (in economy).”

The thickness of the fire under the boiler should be in accordance with the quality and size of the fuel. For hard coal the fire should be as thin as possible, from three to six inches deep; when soft coal is used, the fire should be thicker, from five to eight inches deep.

If it is required to burn coal dust without any change of grates, wetting the coal is of advantage; not that it increases its heat power, but because it keeps it from falling through the grates or going up the chimneys. The same is true of burning shavings; by watering they are held in the furnace, and the firing is done more easily and with better results.

Stirring the Fire should be avoided as much as possible; firing should be performed evenly and regularly, a little at a time, as it causes waste fuel to disturb the combustion and by making the fuel fall through the grates into the ash pit; hence do not “clean” fires oftener than absolutely necessary.

41

The slower the velocity of the gases before they pass the damper, the more nearly can they be brought down to the temperature of the steam, hence with a high chimney and strong draft the dampers should be kept nearly closed, if the boiler capacity will permit it.

No arbitrary rule can be laid down for keeping fires thick or thin. Under some conditions a thin fire is the best, under others a thick fire gives best economy. This rule, however, governs either case: you must have so active a fire as to give strong radiant heat.

One of the highest aims of an expert fireman should be to keep the largest possible portion of his grate area in a condition to give great radiant heat the largest possible part of the day—using anthracite coal by firing light, quick and often, not covering all of the incandescent coals. Using bituminous coal, hand firing, by coking it very near the dead plate, allowing some air to go through openings in the door, and by pushing toward the bridge wall only live coals—when slicing, to open the door only far enough to work the bar; this is done with great skill in some cases.

Regulating the Draft.—This should be done so as to admit the exact quantity of air into the furnace, neither too much nor too little. It should be remembered that fuel cannot be burned without air and if too much air is admitted it cools the furnace and checks combustion. It is a good plan to decrease the draft when firing or cleaning out, by partly closing the damper or shutting off the air usually admitted from below the grates; this is to have just draft enough to prevent the flame from rushing out when the door is opened.

By luminous flame is generally meant that which burns with a bright yellow to white color. All flame under a boiler is not luminous, sometimes the whole or a part of it will be red or blue. The more luminous the flame, that is to say, the nearer white it is, the better combustion.

42

To determine the temperature of a furnace Fire the following table is of use. The colors are to be observed and the corresponding degrees of heat will be approximately as follows:

That is to say, when the furnace is at a “white heat” the heat equals 2,400 degrees Fahrenheit, etc.

Another method of finding the furnace heat is by submitting a small portion of a particular metal to the heat.

FOAMING IN BOILERS.

The causes are—dirty water, trying to evaporate more water than the size and construction of the boiler is intended for, taking the steam too low down, insufficient steam room, imperfect construction of boiler, too small a steam pipe and sometimes it is produced by carrying the water line too high.

Too little attention is paid to boilers with regard to their evaporating power. Where the boiler is large enough for the water to circulate, and there is surface enough to give off the steam, foaming never occurs.

As the particles of the steam have to escape to the surface of the water in the boiler, unless that is in proportion to the amount of steam to be generated, it will be delivered with such violence that the water will be mixed with it, and cause foaming.

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For violent ebullition a plate hung over the hole where the steam enters the dome from the boiler, is a good thing, and prevents a rush of water by breaking it, when the throttle is opened suddenly.

In cases of very violent foaming it is imperative to check the draft and cover the fires.

The steam pipe may be carried through the flange six inches into the dome—which will prevent the water from entering the pipes by following the sides of the dome as it does.

A similar case of priming of the boilers of the U. S. Steamer Galena was stopped by removing some of the tubes under the smoke stack and substituting bolts.

Clean water, plenty of surface, plenty of steam room, large steam pipes, boilers large enough to generate steam without forcing the fires, are all that is required to prevent foaming.

A high pressure insures tranquillity at the surface, and the steam itself being more dense it comes away in a more compact form, and the ebullition at the surface is no greater than at a lower pressure. When a boiler foams it is best usually to close the throttle to check the flow, and that keeps up the pressure and lessens the sudden delivery.

Too many flues in a boiler obstruct the passage of the steam from the lower part of the boiler on its way to the surface—this is a fault in construction.

An engineer who had been troubled with priming, finally removed 36 of the tubes in the centre of the boiler, so as to centralize the heating effect of the fire, thereby increasing the rapidity of ebullition at the centre, while reducing it at the circumference. The effect of the change was very marked. The priming disappeared at once. The water line became nearly constant, the extreme variation being reduced to two inches.

44

A CHAPTER OF DON’TS.

Which is another way of repeating what has already been said.

48

STEAM GENERATORS.

In the examinations held by duly appointed officers to determine the fitness of candidates for receiving an engineer’s license the principal stress is laid upon the applicant’s knowledge of the parts and true proportions of the various designs of steam boilers, and his experience in managing them.

In fact, if there were no boilers there would be no examinations, as the laws are framed, certificates issued and steam boiler inspection companies formed to assure the public safety in life, limb and property, from the dangers arising from so-called mysterious boiler explosions.

Hence an almost undue proportion of engineers’ examinations are devoted to the steam boiler, its management and construction. But the subject is worthy of the best and most thoughtful attention. Every year adds to the number of steam boilers in use. With the expanding area and growth of population, the number of steam plants are multiplied and in turn each new steam boiler demands a careful attendant.

There is this difference between the boiler and the engine. When the latter is delivered from the shop and set up, it does its work with an almost unvarying uniformity, while the boiler is a constant care. It is admitted that the engine has reached a much greater state of perfection and does its duty with very much more reliability than the boiler.

Even when vigilant precautions are observed, from the moment a steam boiler is constructed until it is finally destroyed there are numerous insidious agents perpetually at work which tend to weaken it. There is nothing from which the iron can draw sustenance to replace its losses. The atmosphere without and the air within the boiler, the water as it49 enters through the feed-pipe and containing mineral and organic substances, steam into which the water is converted, the sediment which is precipitated by boiling the water, the fire and the sulphurous and other acids of the fuel, are all natural enemies of the iron; they sap its strength, not only while the boiler is at work and undergoing constant strain, but in the morning before fire is started, and at noon, night, Sundays, and other holidays it is preyed upon by these and other corroding agents.

These are the reasons which impress the true engineer with a constant solicitude regarding the daily and even momentary action of the steam generator.

Description.

The Steam Boiler in its simplest form was simply a closed vessel partly filled with water and which was heated by a fire box, but as steam plants are divided into two principal parts, the engine and the boiler, so the latter is divided again into the furnace and boiler, each of which is essential to the other. The furnace contains the fuel to be burnt, the boiler contains the water to be evaporated.

There must be a steam space to hold the steam when generated; heating surface to transmit the heat from the burning fuel to the water; a chimney or other apparatus to cause a draught to the furnace and to carry away the products of combustion; and various fittings for supplying the boiler with water, for carrying away the steam when formed to the engine in which it is used; for allowing steam to escape into the open air when it forms faster than it can be used; for ascertaining the quantity of water in the boiler, for ascertaining the pressure of the steam, etc., all of which, together with the engine and its appliances is called A STEAM PLANT.

The forms in which steam generators are built are numerous, but may be divided into three classes, viz: stationary, locomotive and marine boilers, which terms designate the uses for which they are intended; in this work we have to deal mainly with the first-named, although a description with illustration is given of each type or form.

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AN UPRIGHT STEAM BOILER.

To illustrate the operations of a steam generator, we give the details of an appliance, which may be compared to the letter A of the alphabet, or the figure 1 of the numerals, so simple is it.

Fig. 11, is an elevation of boiler, fig. 12 a vertical section through its axis, and fig. 13 a horizontal section through the furnace bars.

Fig. 11.

Fig. 12.

The type of steam generator here exhibited is what is known as a vertical tubular boiler. The outside casing or shell is cylindrical in shape, and is composed of iron or steel plates riveted together. The top, which is likewise composed of the same plates is slightly dome-shaped, except at the center, which is away in order to receive the chimney a, which is round in shape and formed of thin wrought iron plates. The interior is shown in vertical section in fig. 12. It consists of a furnace chamber, b, which contains the fire. The furnace is formed like the shell of the boiler of wrought iron or steel plates by flanging and riveting. The bottom is occupied by the grating, on which rests the incandescent fuel. The grating consists of51 a number of cast-iron bars, d (fig. 12), and shown in plan in fig. 13, placed so as to have interstices between them like the grate of an ordinary fireplace. The bottom of the furnace is firmly secured to the outside shell of the boiler in the manner shown in fig. 12. The top covering plate cc, is perforated with a number of circular holes of from one and a half to three inches diameter, according to the size of the boiler. Into each of these holes is fixed a vertical tube made of brass, wrought iron, or steel, shown at fff (fig. 12). These tubes pass through similar holes, at their top ends in the plate g, which latter is firmly riveted to the outside shell of the boiler. The tubes are also firmly attached to the two plates, cc, g. They serve to convey the flame, smoke, and hot air from the fire to the smoke box, h, and the chimney, a, and at the same time their sides provide ample heating surface to allow the heat contained in the products of combustion to escape into the water. The fresh fuel is thrown on the grating when required through the fire door, A (fig. 11). The ashes, cinders, etc., fall between the fire bars into the ash pit, B (fig. 12). The water is contained in the space between the shell of the boiler, the furnace chamber, and the tubes. It is kept at or about the level, ww (fig. 12), the space above this part being reserved for the steam as it rises. The heat, of course, escapes into the water, through the sides and top plate of the furnace, and through the sides of the tubes. The steam which, as it rises from the boiling water, ascends into the space above ww, is thence led away by the steam pipe to the engine. Unless consumed quickly enough by the engine, the steam would accumulate too much within the boiler, and its pressure would rise to a dangerous point. To provide against this contingency the steam is enabled to escape when it rises above a certain pressure through the safety-valve, which is shown in sketch on the top of the boiler in fig. 11. The details of the construction of safety-valves will be found fully described in another section of this work, which is devoted exclusively to the consideration of boiler fittings. In the same chapters will be found full descriptions of the various fittings and accessories of boilers, such as the water and pressure gauges, the apparatus for feeding the boiler with water, for producing the requisite draught of air to maintain the combustion, and also the particulars of the construction of the boilers themselves and their furnaces.

Fig. 13.

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THE GROWTH OF THE STEAM BOILER.

After the first crude forms, such as that used in connection with the Baranca and Newcomen engine, and numerous others, the steam boiler which came into very general use was the plain cylinder boiler. An illustration is given of this in figures 14 and 15.

It consists of a cylinder A, formed of iron plate with hemispherical ends B. B. set horizontally in brick work C. The lower part of this cylinder contains the water, the upper part the steam. The furnace D is outside the cylinder, being beneath one end; it consists simply of grate bars e e set in the brick work at a convenient distance below the bottom of the boiler.

Fig. 14.

Fig. 15.

The sides and front of the furnace are walls of brick work, which, being continued upwards support the end of the cylinder. The fuel is thrown on the bars through the door which is set in the front brick work. The air enters between the grate bars from below. The portion below the bars is called the ash pit. The flame and hot gases, when formed, first strike on the bottom of the boiler, and are then carried forward by the draft, to the so-called bridge wall o, which is a projecting piece of brick work which contracts the area of the flue n and forces all53 the products of combustion to keep close to the bottom of the boiler.

Thence the gases pass along the flue n, and return part one side of the cylinder in the flue m (fig. 15) and back again by the other side flue m to the far end of the boiler, whence they escape up the chimney. This latter is provided with a door or damper p, which can be closed or opened at will, so as to regulate the draught.

This boiler has been in use for nearly one hundred years, but has two great defects. The first is that the area of heating surface, that is the parts of the boiler in contact with the flames, is too small in proportion to the bulk of the boiler; the second is, that if the water contains solid matter in solution, as nearly all the water does to a greater or less extent, this matter becomes deposited on the bottom of the boiler just where the greatest evaporation takes place. The deposit, being a non-conductor, prevents the heat of the fuel from reaching the water in sufficient quantities, thus rendering the heating surface inefficient; and further, by preventing the heat from escaping to the water, it causes the plates to become unduly heated, and quickly burnt out.

There is another defect belonging to this system of boiler to which many engineers attach great importance, viz.: that the temperature in each of the three flues n, m, m´ is very different, and consequently that the metal of which the shell of the boiler is composed expands very unequally in each of the flues, and cracks are very likely to take place when the effects of the changes of temperature are most felt. It will be noted that the flames and gases in this earliest type of steam boiler make three turns before reaching the chimney, and as these boilers were made frequently as much as 40 feet long it gave the extreme length of 120 feet to the heat products.

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The Cornish Boiler is the next form in time and excellence. This is illustrated in figures 16 and 17.

It consists also of a cylindrical shell A, with flat ends as exhibited in cuts. The furnace, however, instead of being situated underneath the front end of the shell, is enclosed in it in a second cylinder B, having usually a diameter a little greater than half that of the boiler shell. The arrangement of the grate and bridge is evident from the diagram. After passing the bridge wall the heat products travel along through the internal cylinder B, till they reach the back end of the boiler; then return to the front again, by the two side flues m, m´, and thence back again to the chimney by the bottom of flue n.

In this form of boiler the heating surface exceeds that of the last described by an amount equal to the area of the internal flues, while the internal capacity is diminished by its cubic contents; hence for boilers of equal external dimensions, the ratio of heating surface to mass of water to be heated, is greatly increased. Boilers of this sort can, however, never be made of as small diameters as the plain cylindrical sort, on account of the necessity of finding room inside, below the water level, for the furnace and flue.

Fig. 16.

Fig. 17.

The disadvantage, too, of the deposits mentioned in the plain cylinder is, to a great extent got over in the Cornish boiler, for the55 bottom, where the deposit chiefly takes place, is the coolest instead of being the hottest part of the heating surface.

But the disadvantage of unequal expansion also exists in this type of boiler, as the internal flue in the Cornish system is the hottest portion of the boiler, and consequently undergoes a greater lengthways expansion than the flues. The result is to bulge out the ends, and when the boiler is out of use, the flue returns to its regular size, and thus has a tendency to work loose from the ends to which it is riveted and if the ends are too rigid to move, a very serious strain comes on the points of the flue.

Even while in use the flue of a Cornish boiler is liable to undergo great changes in temperature, according to the state of the fire; when this latter is very low, or when fresh fuel has been thrown on, the temperature is a minimum and reaches a maximum again when the fresh fuel commences to burn fiercely. This constant expansion and contraction is found in practice to also so weaken the tube that it frequently collapses or is pressed together, resulting in great disaster.

This led to the production and adoption of the—

Lancashire Boiler, contrived to remedy this inconvenience and also to attain a more perfect combustion, the arrangement of the furnaces of which is shown in fig. 19 and fig. 20.

It will be observed that there are two internal furnaces instead of one, as in the Cornish type. These furnaces are sometimes each continued as a separate flue to the other end of the boiler as shown in the cuts; but as a rule they emerge into one internal flue. They are supposed to be fired alternately, and the smoke and unburned gases issuing from the fresh fuel are ignited in the flue by the hot air proceeding from the other furnace, the fuel in which is in a state of incandescence. Thus all violent changes in the temperature are avoided, and the waste of fuel due to unburned gases is avoided, if the firing is properly conducted.

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LANCASHIRE BOILER—Fig. 18.

The disadvantage of the Lancashire boiler is the difficulty of finding adequate room for the two furnaces without unduly increasing57 the diameter of the shell. Low furnaces are extremely unfavorable to complete combustion, the comparatively cold crown plates, when they are in contact with the water of the boiler, extinguishing the flames from the fuel, when they are just formed, while the narrow space between the fuel and the crown does not admit the proper quantity of air being supplied above the fuel to complete the combustion of the gases, as they arise.

On the other hand, though this boiler favors the formation of the smoke, it supplies the means of completing the combustion afterwards, as before explained, by means of the hot air from the second furnace.

Fig. 18 (a)

Another disadvantage is the danger of collapsing the internal flue already spoken of; this is remedied by the introduction of what are called the galloway tubes, illustrated in the cut shown on this page, which is a cross section of the water tubes shown in Figs. 18 and 20.

These tubes not only contribute to strengthen the flues but they add to the heating surface and greatly promote the circulation so important in the water space.

Note.

These descriptions and illustrations of the Lancashire boiler are of general value, owing to the fact that very many exhaustive tests and experiments upon steam economy have been made and permanently recorded in connection with this form of steam generator.

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In the Galloway form of boiler the flue is sustained and stiffened by the introduction of numerous conical tubes, flanged at the two ends and riveted across the flue. These tubes, a sketch of which are given in fig. 18 (a), are in free communication with the water of the boiler, and besides acting as stiffeners, they also serve to increase the heating surface and to promote circulation.

Figs. 19, 20.

The illustration (figs. 18, 19 and 20) give all the principal details of a Lancashire boiler fitted with Galloway tubes. Fig. 18 represents a longitudinal section and figs. 19 and 20 shows on a large scale an end view of the front of the boiler with its fittings and also a transverse section. The arrangement of the furnaces, flues, and the Galloway tubes is sufficiently obvious from the drawings. The usual length of these boilers is 27 feet, though they are occasionally made as short as 21 feet.

The minimum diameter of the furnaces is 33 inches, and in order to contain these comfortably the diameter of the boiler should not be less than 7 feet. The ends of the boiler are flat, and are prevented from bulging outwards by being held in place by the furnaces and flues which stay the two ends together and also by the so-called gusset stays e, e. In addition to the latter the flat ends of the boiler have longitudinal rods to tie them together; one of these is shown at A, A, fig. 18.

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The steam is collected in the pipe S, which is perforated all along the top so as to admit the steam and exclude the water spray which may rise to the surface during ebullition. The steam thence passes to the stop valve T outside the boiler and thence to the steam pipes to the engines.

There are two safety valves on top of the boiler on B (fig. 18), being of the dead weight type described hereafter, and the other, C, being a so-called low water safety valve. It is attached by means of a lever and rod to the float F, which ordinarily rests on the surface of the water. When through any neglect, the water sinks below its proper level the float sinks also, causing the valve to open, thus allowing steam to escape and giving an alarm. M is the manhole with its covering plate, which admits of access to the interior of the boiler and H is the mud hole by which the sediment which accumulates all along the bottom is raked out. Below the front end and underneath, the pipe and stay valve are shown, by which the boiler can be emptied or blown off.

On the front of the boiler (fig. 19) are shown, the pressure gauges, the water gauges and the furnace door; K is the feed pipe; R, R, a pipe and cock for blowing off steam. In the front of the setting are shown two iron doors by which access may be gained to the two lower external flues for cleaning purposes.

In the Lancashire boiler it is considered advisable to take the products of combustion, after they leave the internal flues, along the bottom of the boiler, and then back to the chimney by the side. When this plan is adopted the bottom is kept hotter than would otherwise be the case, and circulation is promoted, which prevents the coldest water from accumulating at the bottom.

The Galloway (or Lancashire) boiler is considered the most economical boiler used in England, and is being introduced into the United States with success. The long traverse of heat provided (three turns of about 27 feet each) contributes greatly to its efficiency.

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It may be useful to add the following data relating to this approved steam generator, being the principal dimensions and other data of the boiler shown in fig. 18:

We have thus detailed step by step the improvement of the steam boiler to a point where it is necessary to describe at length the locomotive, the marine, the horizontal tubular and the water tube boilers, which four forms comprehend ninety-nine out of one hundred steam generators in use in the civilized world at the present time.

MARINE BOILERS.

The boilers used on board steamships are of two principal types. The older sort used for steam of comparatively low temperature, viz.: up to 35 lbs. per square inch, is usually made of flat plates stayed together, after the manner of the exterior and interior fire boxes of a locomotive boiler.

Medium high pressure marine boilers, constructed for steam of 60 to 150 lbs. per square inch, are circular or oval in cross section, and are fitted with round interior furnaces and flues like land boilers. There are many variations of marine boilers, adapted to suit special circumstances. Fig. 22 shows a front elevation and partial sections of a pair of such boilers and Fig. 23 shows one of them in longitudinal vertical section.

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THE MARINE STEAM BOILER

Fig. 22.

Fig. 23.

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It will be seen from these drawings that there are three internal cylindrical furnaces at each end of these boilers, making in all six furnaces per boiler. The firing takes place at both ends. The flame and hot gases from each furnace, after passing over the bridge wall enter a flat-sided rectangular combustion chamber and then travel through tubes to the front uptake (i.e. the smoke bonnet or breaching), and so on to the chimney.

The sides of the combustion chambers are stayed to each other and to the shell plate of the boiler; the tops are strengthened in the same manner as the crowns of locomotive boilers, and the flat plates of the boiler shell are stayed together by means of long bolts, which can be lengthened up by means of nuts at their ends. Access is gained to the uptakes for purposes of cleaning, repairs of tubes, etc., by means of their doors on their fronts just above the furnace doors. The steam is collected in the large cylindrical receivers shown above each boiler. The material of construction is mild steel.

The following are the principal dimensions and other particulars of one of these boilers:

• Length from front to back, 20 feet.
• Diameter of shell, 15 feet 6 inches.
• Length of furnace, 6 feet 10 inches.
• Diameter of furnace, 3 feet 10 inches.
• Length of tubes, 6 feet 9 inches.
• Diameter of tubes, 3¹⁄₂ inches.
• No. of tubes, 516.
• Thickness of shell plates, ¹⁵⁄₁₆.
• Thickness of tube plates, ³⁄₄.
• Grate area, 126¹⁄₂ square feet.
• Heating surface, 4015 square feet.
• Steam pressure, 80 lbs. per sq. inch.

Fig. 24 is a sketch of a modern marine boiler, which is only fired from one end, and is in consequence much shorter in proportion to its diameter than the type illustrated in figs. 22 and 23.

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Marine boilers over nine feet in diameter have generally two furnaces, those over 13 to 14 feet, three, while the very largest boilers used on first-class mail steamers, and which often exceed fifteen feet in diameter, have four furnaces.

In the marine boiler the course taken by the products of combustion is as follows; the coal enters through the furnace doors on to the fire-bars, the heat and flames pass over the fire bridge into the flame or combustion chamber, thence through the tubes into the smoke-box, up the up-take and funnel into the air.

Fig. 24.

The fittings to a marine boiler are—funnel and air casings, up-takes and air casings, smoke boxes and doors, fire doors, bars, bridges, and bearers, main steam stop valve, donkey valve, safety valves and drain pipes, main and donkey feed check valves, blow-off and scum cocks, water gauge glasses on front and back of boiler, test water cock for trying density of water, steam cock for whistle, and another for winches on deck.

A fitting, called a blast pipe, is sometimes placed in the throat of the funnel. It consists of a wrought iron pipe, having a conical nozzle within the funnel pointing upwards, the other end being connected to a cock, which latter is bolted on to the steam space or dome of the boiler. It is used for increasing the intensity of the draft, the upward current of steam forcing the air out of the funnel at a great velocity; and the air having to be replaced by a fresh supply through the ash-pits and bars of the furnaces, a greater speed of combustion is obtained than would otherwise be due to simple draft alone.

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Boilers are fitted with dry and wet uptakes, which differ from each other as follows:—The dry uptake is wholly outside the boiler, and consists of an external casing bolted on to the firing end of the boiler, covering the tubes and forming the smoke-box, and is fitted with suitable tube doors. A wet uptake is carried back from the firing ends of the boiler into its steam space, and is wholly surrounded by water and steam. The dry uptake seldom requires serious repair; but the wet uptake, owing to its exposure to pressure, steam, and water, requires constant attention and repair, and is very liable to corrosion, being constantly wetted and dried in the neighborhood of the water-line. The narrow water space between both front uptakes is also very liable to become burnt, owing to accumulation of salt. The flue boilers of many tugs and ferry boats are fitted with wet uptakes.

A superheater is a vessel usually placed in the uptake, or at the base of the funnel of a marine boiler, and so arranged that the waste heat from the furnaces shall pass around and through it prior to escaping up the chimney. It is used for drying or heating the steam from the main boiler before it enters the steam pipes to the engine. The simplest form of superheater consists of a wrought iron drum filled with tubes. The heat or flame passes through the tubes and around the shell of the drum, the steam being inside the drum. Superheaters are usually fitted with a stop valve in connection with the boiler, by means of which it can be shut off; and also one to the steam pipe of the engine; arrangements are also usually made for mixing the steam or working independently of the superheater.

A safety-valve is also fitted and a gauge glass; the latter is to show whether the superheater is clear of water, as priming will sometimes fill it up.

The special fittings of the marine boiler will be more particularly described hereafter as well as the stays, riveting, strength, etc., etc.

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The use of the surface condenser in connection with the marine boiler was an immense step toward increasing its efficiency. In 1840 the average pressure used in marine boilers was only 7 or 8 lbs. to the square inch, the steam being made with the two-flue pattern of boiler, sea water being used for feed; as the steam pressure increased as now to 150 to 200 lbs. to the square inch, greater and greater difficulty was experienced from salt incrustation—in many cases the tubes did not last long and frequently gave much trouble, until the introduction of the surface condenser, which supplied fresh water to the boilers.

Fig. 25

The Surface Condenser.

The condenser is an oblong or circular box of cast iron fitted in one of two ways, either with the tubes horizontal or vertical; at each end are fixed the tube plates, generally made of brass, and the tubes pass through the plates as well as through a supporting plate in the middle of the condenser. Each end of the condenser is fitted with doors for the purpose of enabling the tube ends to be examined, drawn, or packed, as may be necessary. The tube ends are packed in various ways, and the tubes are made of brass, so as to resist the action of the water. The water is generally sucked through the tubes by66 the circulating pump, and the steam is condensed by coming in contact with the external surface of the tubes. In some cases the water is applied to the external surface, and the steam exhausted through the tubes; but this practice is now generally given up in modern surface condensers. The packing round the tube ends keeps them quite tight, and in the event of a split tube, a wooden plug is put in each end until an opportunity offers for drawing it and replacing with a new one.

The condenser may be made of any convenient shape. It sometimes forms part of the casting supporting the cylinders of vertical engines; it is also frequently made cylindrical with flat ends, as in fig. 25. The ends form the tube plates to which the tubes are secured. The tubes are, of course, open at the ends, and a space is left between the tube plate and the outer covers, shown at each end of the condenser, to allow of the circulation of water as shown by the arrows.

Operation of the Condenser.

The cold water, which is forced through by a circulating pump, enters at the bottom, and is compelled to pass forward through the lower set of tubes by a horizontal dividing plate; it then returns through the upper rows of tubes and passes out at the overflow; the tubes are thus maintained at a low temperature.

The tubes are made to pass right through the condensing chamber, and so as to have no connection with its internal space. The steam is passed into the condenser and there comes in contact with the cold external surface of the tube, and is condensed, and removed as before, by the air pump, as may be readily seen in the illustration (p. 65.)

The advantages gained by the use of the surface condenser are: 1. The feed water is hotter and fresh; being hotter, it saves the fuel that would be used to bring it up to this heat; and being fresh it boils at a lower temperature. 2. Not forming so much scale inside the boiler, the heat passes through to the water more readily; and as the scum cock is not used so freely, all the heat that would have been blown off is saved. Its disadvantages are that being fresh water and forming no scale on the boiler, it causes the boiler to rust.

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It is often said that one engineer will get more out of a ship than another. In general it will be found that the most successful engineer is the man who manages his stokers best. It is very difficult on paper to define what is meant. It is a thing to be felt or seen, not described. * * * * The engineer who really knows his business will give his fires a fair chance to get away. He will work his engines up by degrees and run a little slowly for the first few moments.

WATER TUBE STEAM BOILERS.

Water Tube Boiler.—Fig. 26.

A popular form of steam boiler in use in the United States and Europe is what is called the water tube boiler. This term is applied to a class of boiler in which the water is contained in a series of tubes, of comparatively small diameter, which communicate with each other and with a common steam-chamber. The flames and hot gases circulate between the tubes and are usually guided by partitions so as to act equally on all portions of the tubes. There are many varieties of this type of boiler of which the cut illustrates one: in this each tube is secured at either end into a square cast-iron head, and each of these heads has two openings, one communicating with the tube below and the other with the tube above; the68 communication is effected by means of hollow cast-iron caps shown at the end of the tubes; the caps have openings in them corresponding with the openings in the tube heads to which they are bolted.

In the best forms of the water tube boilers, it is suspended entirely independent of the brick work from wrought iron girders resting on iron columns. This avoids any straining of the boiler from unequal expansion between it and its enclosing walls and permits the brick work to be repaired or removed, if necessary, without in any way disturbing the boiler. This design is shown in Fig. 26.

The distinguishing difference, which marks the water tube boiler from others, consists in the fact that in the former the small tubes are filled with water instead of the products of combustions; hence the comparison, frequently made, between water-tube and fire tube boilers—the difference has been expressed in another way, “Water-tube vs. shell boilers,” but the principle of steam production in both systems remains the same; the heat from the combustible is transferred to the water through the medium of iron plates and in both, the furnaces, steam appliances, application of the draught, etc., is substantially the same. In another important point do the systems agree, i.e., in the average number of pounds of water evaporated per lb. of combustible; it is in the thoroughness of construction and skillfulness of adaptation to surroundings that produce the best results. Water tube or sectional boilers, have been made since the days of James Watt, in 1766, in many different forms and under various names. Owing, however, to the imperfection of manufacture the system, as compared to shell boilers, has been a failure until very recently; various patterns of water-tube boilers are now in most favorable and satisfactory use. The advantages claimed for this form of steam generator are as follows:

1. Safety from disastrous explosions, arising from the division of the contents into small portions, and especially from details of construction which make it tolerably certain that the rupture will be local instead of a general violent explosion which liberates at once large masses of steam and water.

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2. The small diameter of the tubes of which they are composed render them much stronger than ordinary boilers.

3. They can be cheaply built and easily repaired, as duplicate pieces can be kept on hand. The various parts of a boiler can be transported without great expense, trouble or delay; the form and proportions of a boiler can be suited to any available space; and, again, the power can be increased by simply adding more rows of tubes and increasing the grate area.

4. Their evaporative efficiency can be made equal to that of other boilers, and, in fact, for equal proportions of heating and grate surfaces, it is often a trifle higher.

5. Thin heating surface in the furnace, avoiding the thick plates necessarily used in ordinary boilers which not only hinder the transmission of heat to the water, but admit of overheating.

6. Joints removed from the fire. The use of lap welded water tubes with their joints removed from the fire also avoid the unequal expansion of riveted joints consequent upon their double thickness.

7. Quick steaming.

8. Accessibility for cleaning.

9. Ease of handling and erecting.

10. Economy and speediness of repairs.

The known disadvantages of these boilers are

1. They generally occupy more space and require more masonry than ordinary boilers.

2. On account of the small quantity of water which they contain, sudden fluctuations of pressure are caused by any irregularities in supplying the feed-water or in handling the fires, and the rapid and at times violent generation of steam causes it to accumulate in the contracted water-chambers, and leads to priming, with a consequent loss of water, and to overheated tubes.

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3. The horizontal or inclined water tubes which mainly compose these boilers, do not afford a ready outlet for the steam generated in them. The steam bubbles cannot follow their natural tendency and rise directly, but are generally obliged by friction to traverse the tube slowly, and at times the accumulation of steam at the heated surfaces causes the tubes to be split or burned.

4. The use of water which forms deposits of solid matter still further increases the liability to overheating of the tubes. It has been claimed by some inventors that the rapid circulation of the water through the tubes would prevent any deposit of scale or sediment in them, but experience has proved this to be a grave error. Others have said that the expansion of the tube would detach the scale as fast as it was deposited and prevent any dangerous accumulation, but this also has been proved an error. Again, the use of cast iron about these boilers has frequently been a constant source of trouble from cracks, etc.

CARE OF WATER TUBE BOILERS.

The soot and ashes collect on the exterior of the tubes in this form of boilers, instead of inside the tubes, as in the tubular, and they must be as carefully removed in one case as in the other; this can be done by the use of blowing pipe and hose through openings left in the brick work; in using bituminous coal the soot should be brushed off when steam is down.

All the inside and outside surfaces should be kept clean to avoid waste of fuel; to aid in this service the best forms are provided with extra facilities for cleaning. For inspection, remove the hand holes at both ends of the tubes, and by holding a lamp at one end and looking in at the other the condition of the surface can be freely seen. Push the scraper through the tube to remove sediment, or if the scale is hard, use the chipping scraper made for that purpose.

Hand holes should be frequently removed and surfaces examined, particularly in case of a new boiler. In replacing71 hand hole caps, clean the surfaces without scratching or bruising, smear with oil and screw up tight.

The mud drum should be periodically examined and the sediment removed; blow-off cocks and check valves should be examined each time the boiler is cleaned; when surface blow-cocks are used they should be often opened for a few minutes at a time; be sure that all openings for air to boiler or flues except through the fire, are carefully stopped.

If a boiler is not required for some time, empty and dry it thoroughly. If this is impracticable, fill it quite full of water and put in a quantity of washing soda; and external parts exposed to dampness should receive a coating of linseed oil. Avoid all dampness in seatings or coverings and see that no water comes in contact with the boiler from any cause.

Although this form of boiler is not liable to destructive explosion, the same care should be exercised to avoid possible damage to boilers and expensive delays.

SECTIONAL BOILERS.

Probably one of the first sectional boilers brought into practical use is one made of hollow cast iron spheres, each 8 inches in diameter, externally, and ³⁄₈ of an inch thick, connected by curved necks 3¹⁄₂ inches in diameter. These spheres are held together by wrought iron bolts and caps, and in one direction are cast in sets of 2 or 4, which are afterwards drawn together so as to give more or less heating surface to the boiler according to the number used.

NOTE.

Owing to their multiplication of parts all sectional, including water tube boilers, should be made with unusual care in their details of construction, setting, fittings and proportions. It is to the attention paid to these “points” that the sectional boilers are now coming into more general favor.

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LOCOMOTIVE BOILERS.

The essential features of locomotive boilers are dictated by the duties which they have to perform under peculiar conditions. The size and the weight are limited by the fact that the boiler has to be transported rapidly from place to place, and also that it has to fit in between the frames of the locomotive; while at the same time, the pressure of the steam has to be very great in order that with comparatively small cylinder the engine may develop great power; moreover, the quantity of water which has to be evaporated in a given time is very considerable. To fulfil these latter conditions a large quantity of coal must be burned on a fire grate of limited area; hence intense combustion is necessary under a forced blast. To utilize advantageously the heat thus generated, a large heating surface must be provided and this can only be obtained by passing the products of combustion through a great number of tubes of small diameter.

The forced draught in a locomotive boiler is obtained by causing the steam from the cylinders, after it has done its work, to be discharged into the chimney by means of a pipe called the blast pipe; the lower portion of this consists of two branches, one in communication with the exhaust port of each cylinder. As each puff of steam from the blast pipe escapes up the chimney it forces the air out in front of it, causing a partial vacuum, which can only be supplied by the air rushing through the furnace and tubes.

The greater the body of steam escaping at each puff, and the more rapid the succession of puffs, the more violent is the action of the blast pipe in producing a draught, and consequently this contrivance regulates the consumption of fuel and the evaporation of water to a certain extent automatically, because when the engine is working its hardest and using the most steam, the blast is at the same time most efficacious.

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LOCOMOTIVE BOILER.—Fig. 27.

The blast pipe is perhaps, the most distinctive feature of the locomotive boiler, and the one which has alone rendered it possible to obtain large quantities of steam from so small a74 generator. The steam blast of a locomotive has been compared to the breathing apparatus of a man, and has rendered the mechanism described nearer a live thing than any other device man has ever produced.

On account of the oscillations, or violent motions to which the boiler of locomotive engines are subject, weighted safety-valves are not possible to be used and springs are used instead to hold the valves in place.

The locomotive form of steam boiler is sometimes used for stationary engines, but owing to extra cost and increased liability to corrode in the smaller passage they are not favorites.

DESCRIPTION OF PAGE ILLUSTRATION.

In fig. 27, F B represents the fire box or furnace; F D, fire door; D P, deflector plate; F T P, fire box tube plate; F B R S, fire box roof stays; S T P, smoke box tube plate; S B, smoke box; S B D, smoke box door; S D, steam dome; O S, outer shell; R S V, Ramsbottom safety-valve; F, funnel or chimney.

Fig. 28.

The crown plate of the fire-box being flat requires to be efficiently stayed, and for this purpose girder stays called fox roof stays are mostly used, as shown in the figure. The stays are now made of cast steel for locomotives. They rest at the two ends on the vertical plates of the fire-box, and sustain the75 pressure on the fire-box crown by a series of bolts passing through the plate and girder stay, secured by nuts and washers. Fig. 28 is a plan and elevation of a wrought-iron roof stay.

Another method adopted in locomotive types of marine boilers for staying the flat crown of the fire-box to the circular upper plate is shown in fig. 29—namely, by wrought-iron vertical bar stays secured by nuts and washers to the fire-box with a fork end and pin to angle-iron pieces riveted to the boiler shell.

Fig. 29.

The letters in this figure refer to the same parts of the boiler as do those in fig. 27, i.e., F B to the fire-box, etc., etc.

It was formerly the custom to make the tubes much longer than shown in the fig., with the object of gaining heating surface; but modern experience has shown that the last three or four feet next the smoke box were of little or no use, because, by the time the products of combustion reached this part of the heating surface, their temperature was so reduced that but little additional heat could be abstracted from them. The tubes, in addition to acting as flues and heating surface, fulfil also the function of stays to the flat end of the barrel of the boiler, and the portion of the fire box opposite to it.

In addition to the staying power derived from the tubes, the smoke box, tube plate and the front shell plate are stayed together by several long rods.

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The Horizontal Tubular Boiler.—Fig. 30.

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STANDARD HORIZONTAL TUBULAR STEAM BOILER.

TABLE OF SIZES, PROPORTIONS, ETC.:

Note.

In estimating the horse power by means of the above table, 15 square feet has been allowed for each horse power, and the number of feet in each boiler is given in round numbers. This table is one used in every-day practice by boiler makers.

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THE FLUE BOILER.

The Two Flue Boiler.—Fig. 31.

The Six Inch Flue Boiler.—Fig. 32.

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THE HORIZONTAL TUBULAR STEAM BOILER.

The great majority of stationary boilers are cylindrical or round shaped, because—

1. The cylindrical form is the strongest.

2. It is the cheapest.

3. It permits the use of thinner metal.

4. It is the safest.

5. It is inspected without difficulty.

6. It is most symmetrical.

7. It is manufactured easier.

8. It resists internal strain better.

9. It resists external strain also.

10. It can be stayed or strengthened better.

11. It encloses the greatest volume with least material.

12. It is the result of many years’ experience in boiler practice.

13. It is the form adopted or preferred by all experienced engineers.

It follows, too, that the horizontal tubular boiler, substantially as shown in fig. 30, is the standard steam boiler; engineers and steam power owners cling with great tenacity to this approved form, which is an outgrowth of one hundred years’ experience in steam production.

In the plain horizontal tubular boiler shown in cuts, the shell is filled with as many small tubes varying from two inches to four inches in diameter as is consistent with the circulation and steam space. In firing this type of boiler the combustion first takes place under the shell, and the products, such as heat, flame, and gas, pass through the small tubes to the chimney, although in the triple draught pattern of the tubular boiler, the heat products pass, as will hereafter be explained, a second time through the boiler tubes, making three turns before the final loss of the extra heat takes place.

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The illustrations on pages 78 and 80 exhibit the gradual advances to the horizontal tubular by the two-flued boiler (fig. 31) of the six flues (fig. 32) and of the locomotive Portable Boiler (fig. 33). The vertical or upright tubular boiler is but another modification of the horizontal tubular.

The Locomotive Portable Boiler.—Fig. 33.

In parts of the vertical boiler there is very little circulation and the corrosion on the inner side is such as to wear the boiler rapidly. In the ash pit, ashes and any dampness that may be about the place also causes rapid corrosion. The upper part of the tubes and tube sheet are frequently injured; for instance, if the tubes pass all the way through to the upper tube sheet, providing there is no cone top, when the fire is first made under the boiler, combustion at times does not take place until the gases pass nearly through the tubes. The water usually being carried below the tube sheet there is a space left above the water line, where there is neither steam nor water, and the heat is so great that the ends of the tubes are burned and crystalized, and the tube sheet is often cracked and broken by this excessive heat before the steam is generated. The first difficulty is experienced in “the legs” of the Portable Locomotive boiler—hence the general verdict of steam users in favor of the round shell, many-tubed boiler.

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PARTS OF THE TUBULAR BOILER.

The Shell. This is the round or cylindrical structure which is commonly described as the boiler, in which are inserted the braces and tubes, and which sustains the internal strain of the pressure of the steam, the action of the water within, and the fire without.

The Drum. This part is sometimes called the dome, and consists of an upper chamber riveted to the top of the boiler for the purpose of affording more steam space.

The Tube Sheets. These are the round, flat flanged sheets forming the two ends of the boiler, into which the tubes are fastened.

The Manhole Cover. This is a plate and frame commonly opening inwards and large enough to admit a man into the interior of the boiler. These openings are sometimes made on the top and sometimes at the end of the boiler. Manhole openings in steam boilers should invariably be located in the head of the boiler, except in rare cases that may arise, when circumstances require it to be placed in the shell. The manhole, so placed, will not materially reduce the strength of the boiler, and from this position it can more readily be seen that the boiler is kept in proper condition. The proper sizes for manholes are 9×5 and 10×16, according to circumstances. These are amply large for general use and no material advantage is gained by increasing them.

The Hand Hole Plates. These are similar arrangements to the manhole cover, except as to size. They are made large enough to admit the hand into the boilers for the purpose of removing sediment and they are also used for the purpose of inspecting the interior of the boiler. Two are usually put in each boiler, one front and one in the rear.

The Blow Off. This consists of pipes and a cock communicating with the bottom of the boiler for the purpose of blowing off the boiler or of running off the water when the former needs cleaning.

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THE TRIPLE DRAUGHT TUBULAR BOILER.—Fig. 34.

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THE TRIPLE DRAUGHT TUBULAR BOILER.

This boiler, which is extensively used by the manufacturers of New England, is, as will be seen by the illustration, of the horizontal tubular class, and is essentially different from the well known type only in the arrangement of the tubes. The method secures the passage of the products of combustion through the same shell twice; forward through a part of the tubes, and backwards through the remaining ones. The manner of accomplishing this result can be best described by explaining how a common tubular boiler may be remodelled so as to carry out this principle.

Fig. 35.

A cylindrical shell, as shown in Fig. 34—of sufficient size to encircle about one-half of the tubes, is attached to the outside of the rear head below the water line, and extended backward to the back end of the setting. The encircled tubes are lengthened and carried backward to the same point; the extension is closed in and made to communicate with the boiler proper; the inner tubes emerge to the flue leading to the chimney and the old connection from the smoke arch is cut off. With this arrangement, the outer tubes of the boiler—a cluster on each side of the supplementary shell carry the products of combustion forward to the front smoke arch, and the inner tubes carry them backward to the chimney.

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Fig. 35 exhibits the boiler in half section and shows the course of the heat products through one of the outer tubes and returning through the boiler by one of the inner cluster.

Fig. 36 (page 84) shows the boiler sectionally, over the bridge wall; the shaded tube ends exhibit the cluster which return the heat products to the rear of the boiler, after being brought forward by the two outer clusters which are left unshaded.

This arrangement of the tubes gives several advantages:

1. It enables an exceedingly high furnace temperature, without loss at the chimney.

2. By dividing the heat into these currents a more equal expansion and contraction is secured. This is an important point secured.

3. In this system the tubes are almost equally operative.

4. The extra body of water immediately over the furnace is both an element of safety and a reservoir of power.

5. The outlet for the waste products of combustion is found in this style of boiler in a more convenient position at the rear end of the boiler.

6. The boiler being self-contained, can be used in places where height of story is limited.

Fig. 36.

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SPECIFICATION FOR 125 HORSE POWER BOILER.

For one Horizontal Tubular Boiler 72 inches diameter 18 feet long for…………………of………

Type.

The boiler to be of the Horizontal Tubular type with all castings and mountings complete.

Dimensions.

Boiler 72 inches diameter and 18 feet long. Each boiler to contain 90 best lap welded tubes 3¹⁄₂ inches diameter by 18 feet long, set in vertical and horizontal rows with a space between them vertically and horizontally of no less than one inch and one-quarter (1¹⁄₄) except central vertical space, which is to be three inches (3). No tube to be nearer than two and one-half inches (2¹⁄₂) to shell or boiler. Holes through heads to be neatly chamfered off. All tubes to be set by Dudgeon Expander and slightly flared at front end, turned over and beaded down at back end.

Quality and Thickness of Steel Plates.

Shell plates to be ¹⁄₂-inch thick of homogeneous steel of uniform quality having a tensile strength of not less than 65,000 lbs. Name of maker, brand and tensile strength to be plainly stamped on each plate.

Heads to be of same quality as plates of shell in all particulars ³⁄₄-inch thick. Bottom of shell to be of one plate, and no plate to be less than 7 feet wide. Top of shell to be in three plates. All plates planed before rolling, and all joints fullered not caulked.

Flanges.

All flanges to be turned in a neat manner to an internal radius of not less than two inches (2) and to be clear of cracks, checks or flaws.

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Riveting.

Boilers to be riveted with ³⁄₄-inch rivet throughout. All girth seams to be double riveted. All horizontal seams to be double riveted. Rivet holes to be punched or drilled so as to come fair in construction. No drift pins to be used in construction of the boilers.

Braces.

All braces to be of the crowfoot pattern, one and one eighth (1¹⁄₈) inch diameter and the shortest to be no less than four feet (4) long and of sufficient number for thorough bracing, and to bear uniform tension.

Manholes, Hand Holes and Thimbles.

One manhole in top of each boiler with heavy cast iron frame riveted on middle of centre plate; one manhole near the bottom of each front head; head reinforced with a wrought iron ring two inches (2) square, riveted to heads with flush countersunk rivets two inches (2) pitch and to have all the necessary bolts, plates, guards and gaskets; two six-inch thimbles riveted to top of each boiler, each to have a planed face; one heavy 6-inch flange on bottom of each boiler, 12 inches from back end to centre of flange. There must be two braces, one on each side of manhole in front head; also to have three braces opposite manhole on back head below tubes.

Lugs.

Four (4) lugs riveted on each side of boilers, of good and sufficient size, with six one-inch rivets in each lug.

Castings.

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Each boiler to have a complete set of castings consisting of ornamental flush fronts containing tube, fire and ash-pit doors, and provide the best stationary grate bars as may be selected by buyer, with the necessary fixtures, all bearing bars, britching plates, dead plates, binder bars, back cleaning out doors with frames. Anchor bolts and buck stays. The fire door to contain adjustable air opening and to be protected with fire shields. One heavy cast iron arch over each boiler.

Testing.

Boilers to be tested with a water pressure of 200 lbs. per square inch and certificate of such test having been made shall be furnished with boiler. Test of boiler to be under direction of such steam boiler Insurance Company as may be selected by buyer.

Quality and Workmanship.

All boilers to be made in the best workmanlike manner and all material of their respective kinds to be of the best, and in strict accordance with specification.

Fittings and Mountings.

The boiler to be furnished with the following: One four inch heavy mounted safety valve. One six inch flanged globe valve. Two two inch best globe valves. Two two inch check valves. One eight inch dial nickel plated steam gauge. One low water alarm gauge. One set of fire irons for two boilers consisting of hoe, poker, slice bar and shovel.

Drawings.

All drawings furnished for masons in setting the boilers.

Duty of Boiler.

The boiler to develop 120 horse power and to work under a constant pressure varying from 125 to 150 lbs. to the square inch.

All rivets are to be 2¹⁄₂ and 1¹⁄₂ inch pitch. The pitch line of the rivets to be not nearer 1¹⁄₈ inches to the edge of the sheet.

To be 8 lug plates for each boiler not less than 2 feet long, 8 inches wide, and one inch thick.

There shall be six 1 inch anchor rods running front to rear of each boiler, in the brick work.

These boilers and all their fronts, fittings and connections will be subject to the inspection of…………………

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MARKS ON BOILER PLATES.

Something has been said under another heading of the nature and requisite quality of the materials entering into the structure of the boiler. Too much emphasis cannot be laid upon the necessity for the use of the very best iron and steel that can be manufactured, and the most skillful and thorough workmanship that can be performed in constructing the boiler.

It is becoming the practice, both for land and marine boilers, for boiler plate makers to furnish “test pieces” from each sheet or plate that goes into the construction of a boiler, and a sheet showing the tensile strength of each sheet or plate that enters into its make up.

But irrespective of this practice each plate entering into boiler construction will be found to have one of the following marks, which designate its quality and method of manufacture. The name “Charcoal Iron” is used because in its manufacture wood charcoal is employed instead of mineral fuel.

“Charcoal No. 1 Iron” (C. No. 1) is made entirely of charcoal iron. It has a tenacity of 40,000 pounds per square inch in the direction of the fibre. It is hard, but not very ductile, and should never be used for flanging.

“Charcoal Hammered No. 1 Shell Iron” (C. H. No. 1 S.), although not necessarily hammered, has been worked up before it is rolled into plates. It has a tenacity of 50,000 to 55,000 pounds per square inch in the direction of the fibre. It is rather hard iron, and should not be flanged. It is used for the outside shell of boilers.

“Flange Iron” (C. H. No. 1 F.), is a ductile material which can be flanged in every direction. It has a tenacity of 50,000 to 55,000 pounds per square inch along the fibre.

“Fire Box Iron” (C. H. No. 1 F. B.), is a harder quality, designed especially to withstand the destructive effect of the impinging flame, and is used for boxes and flue-sheets.

The letters in the brackets exhibit the plate stamp.

Cast iron and copper were used in an early day for steam boilers and the former is still extensively used for certain forms of low pressure steam heaters made for various purposes, such as green houses, etc.

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CONSTRUCTION OF BOILERS.

In selecting a boiler, the most efficient design will be found to be that in which the greatest amount of shell surface is exposed to direct heat. It is the direct heating surface that does the bulk of the work and every tendency to reduce it, either in the construction or setting of the boiler, should be avoided. The smaller the amount of surface enclosed by or in contact with the setting, the better results will be obtained.

A boiler with a bad circulation is the bane of an engineer’s existence. Proper circulation facilities constitute one of the chief factors in the construction of a successful and economical boiler. In tubular boilers the best practice places the tubes in vertical rows, leaving out what would be the centre row. The circulation is up the sides of the boiler and down the centre. Tubes set zig-zag to break spaces impede the circulation and are not considered productive of the best results.

The surface from which evaporation takes place should be made greater as the steam pressure is reduced, that is to say, as the size of the bubbles of steam become greater. To produce 100 lbs. of steam per hour at atmospheric pressure this surface should not be less than 732 square feet, which may be reduced to 146 square feet for steam at 75 lbs. pressure, and to 73 feet for steam at a pressure of 150 lbs. It is for this reason that triple-expansion engines can be worked with smaller boilers than are required with engines using steam of lower pressure. The amount of steam space to be permitted depends upon the volume of the cylinders and the number of revolutions made per minute. For ordinary engines it may be made a hundred times as great as the average volume of steam generated per second.

A volume of heated water in a boiler performs the same office in furnishing a steady supply of steam as a fly-wheel does to an engine in insuring uniformity of speed; hence the centre space of a boiler should be ample, in order to take advantage of this reserve force.

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QUALITY OF STEEL PLATES.

Steel for boilers is always of the kind known as low steel, or soft steel, and is, properly speaking, ingot iron, all of its characteristics being those of a tenacious, bending, equal grained iron, and quite different from true steels, such as knife blades, cutting tools, etc., are composed of. Steel is rapidly displacing iron in boiler construction, as it has greater strength for the same thickness, than iron; and, except in rare instances, where the nature of the water available for feed renders steel undesirable, iron should not be used for making boilers, careful tests having shown it to be vastly inferior to steel in many important features.

Good boiler steel up to one-half inch in thickness should be capable of being doubled over and hammered down on itself without showing any signs of fracture, and above that thickness it should be capable of being bent around a mandrel of a diameter equal to one and one-half times the thickness of the plate, to an angle of 180 degrees without sign of distress. Such bending pieces should not be less in length than sixteen times the thickness of the plate.

On this test piece the metal should show the following physical qualities:

Tensile strength, 55,000 to 65,000 pounds per square inch.

Elongation, 20 per cent. for plates three-eighths inch thick or less.

Elongation, 22 per cent. for plates from three-eighths to three-fourths inch thick.

Elongation, 25 per cent. for plates over three-fourths inch thick.

The cross sectional area of the test piece should be not less than one-half of one square inch, i.e., if the piece is one-fourth inch thick, its width should be two inches; if it be one-half inch thick, its width should be one inch. But for heavier material the width shall in no case be less than the thickness of the plate.

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Nickel Steel Boiler Plates.

It has been found that the addition of about three per cent. (3.16 to 3.32) of nickel to ordinary soft steel produces most favorable results; thus it has been shown by Riley that a particular variety of nickel steel presents to the engineer the means of nearly doubling boiler pressures without increasing weight or dimensions.

In a recent experiment made with Bessemer steel rolled into three-fourths inch plates from which a number of test specimens were cut, the elastic limit was respectively 59,000 pounds and 60,000 pounds. The ultimate tensile strength was 100,000 pounds and 102,000 pounds, respectively. The elongation was 15¹⁄₂ per cent. in each specimen, and the reduction of area at fracture was 29¹⁄₂ per cent. and 26¹⁄₂ per cent. respectively. These figures show that the elastic limit and ultimate tensile strength was raised by the nickel alloy to almost double the limits reached in the best grades of boiler plate steel, and the elongation was reduced to a scarcely appreciable extent.

The experiment had for its object, the reproduction, as nearly as possible, of the alloy used in the nickel steel armor plate made at Le Creusot, France, and the result was reported to the Secretary of the Navy at Washington. The new plate showed a percentage of 3.16 nickel, as against 3.32 for the imported plate.

RIVETING.

When the materials are of best quality, then there only remains to rivet and stay the boiler. Riveting is of two kinds, single and double. Fig. 37 shows the method of single riveting, and Figs. 38 and 39 show the plan and cross-section of double riveted sheets.

Fig. 37.

Double Riveting consists in making the joints of boiler work with two rows of rivets instead of one—nearly always, horizontal seams are double riveted as well as domes where they join upon the boiler. Usually all girth92 seams,—those running round the body of the boiler, are single riveted. The size of the rivets is in proportion to the diameter of the boiler, being ⁵⁄₈, ³⁄₄ and ⁷⁄₈ as required in the specification.

Rivet holes are made by punching or drilling, according to the material in which they are made. In soft iron and mild steel they may safely be punched, but in metal at all brittle the holes should be drilled.

Fig. 38.

Rivets are driven by hand, by steam riveting machines or by an improved pneumatic machine which holds the sheet together and strikes a succession of light blows to form the head of the rivet while hot. Rivets are made both of iron and steel, and there are certain well-known brands of such excellent quality that they are almost exclusively used in boiler work.

A place where skill is shown in boiler construction is in laying out the rivet holes, with a templet, so that the sheets come exactly together with the holes so nearly opposite that the dreaded drift pin does not have to be used.

In these figures the letters P and p refer to the “pitch of the rivets,” i.e., the part from centre to centre, and the dimensions given at the sides indicate the amount of lap given in inches and tenths of inches—the diameter of the rivet (1″) is also shown, and the turned over portion of the shank of the rivet is shown by dotted lines.

Fig. 39.

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No riveted boiler work can be considered fairly proportioned unless the strength of the plate between the rivets is fully equal to the strength of the rivets themselves. A margin (or net distance from outside of holes to edge of plate) equal to the diameter of the drilled hole has been found sufficient.

Rivets should be made of good charcoal iron or of a very soft mild steel, running between 50,000 and 60,000 pounds tensile strength and showing an elongation of not less than ninety per cent. in eight inches, and having the same chemical composition as specified for plates.

A long rivet, holding thick plates together, is rarely tight except immediately under the head. The heads are set and the centre cooled before the hole is properly filled. If it is a very long rivet there is a chance of the contraction fracturing the head of the rivet. In the Forth Bridge, which is made of very heavy plate girders, the rivets, first carefully fitted, were driven tight into the holes, the burr around the holes were removed, and the ends of the rivets heated to a sufficient degree to enable them to be closed over.

A simple mathematical deduction shows that a circle seam has just one-half the strain to carry as a longitudinal seam, under the same pressure and with the same thickness of metal, hence the custom of single riveting the former and double riveting the latter, or longwise seams.

Different Modes of Riveting.

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In fig. 41 may be seen an example of zig-zag riveting.

Fig. 41.

Caulking.—By this is meant the closing of the edges of the seams of boilers or plates. In preparing the seams for caulking, the edges are first planed true inside and outside; and after the plates have been riveted together, the edges are caulked or closed by a blunt chisel about ¹⁄₄-inch thick at the edge, which should be struck with a 3 or 4-lb. hammer; sometimes one man doing the work alone and sometimes one holding the chisel and another striking.

Fullering a boiler plate is done by a round-nosed tool, while caulking is executed by a sharper instrument.

The thinnest plate which should be used in a boiler is one-fourth of an inch, on account of the almost impossibility of caulking the seams of thinner plates.

It is a rule well known to all practical boiler makers that the thinner the metal (compatible with due strength) the longer the life of the boiler under its varying stresses and the better the caulking will stand.

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STEEL RIVETS.

Hitherto there has been some prejudice against steel rivets, and while this may have some foundation when iron plates are used, it is certainly baseless when steel plates are concerned. The United States government has clearly demonstrated this. All the ships of the new navy have steel boilers, riveted with steel rivets, and an examination of the character of the material prescribed and the severity of the tests to which it is subjected show that these steel-riveted steel boilers are probably the best boilers ever constructed.

United States Government Requirements for Boiler Rivets.

They are subjected to the most severe hammer tests, such as flattening out cold to a thickness of one-half the diameter, and flattening out hot to a thickness of one-third the diameter. In neither case must they show cracks or flaws.

Kind of Material.—Steel for boiler rivets must be made by either the open-hearth or Clapp-Griffith process, and must not show more than .035 of one per centum of phosphorus nor more than .04 of one per centum of sulphur, and must be of the best quality in other respects.

Each ton of rivets from the same heat or blow shall constitute a lot. Four specimens for tensile tests shall be cut from the bars from which the lot of rivets is made.

Tensile Tests.—The rivets for use in the longitudinal seams of boiler shells shall have from 58,000 to 67,000 pounds tensile strength, with an elongation of not less than 26 per centum; and all others shall have a tensile strength of from 50,000 to 58,000 pounds, with an elongation of not less than 30 per centum in eight (8) inches.

Hammer Test.—From each lot twelve (12) rivets are to be taken at random and submitted to the following tests:

Four (4) rivets to be flattened out cold under the hammer to a thickness of one-half the diameter without showing cracks or flaws.

Four (4) rivets to be flattened out hot under the hammer to a thickness of one-third the diameter without showing cracks or flaws—the heat to be the working heat when driven.

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Four (4) rivets to be bent cold into the form of a hook with parallel sides, without showing cracks or flaws.

Surface Inspection.—Rivets must be true to form, free from scale, fins, seams and all other unsightly or injurious defects.

In view of the fact that the government is using many hundred tons of these rivets, shown by the records of the tests to be vastly superior to any iron rivet made, in all the essentials of a good rivet, it would seem that it would benefit the boiler maker, the purchaser of the boiler and also the maker of the rivet by adopting a standard steel rivet to be used in all steel boilers.

BRACING OF STEAM BOILERS.

The material of a boiler being satisfactory and the plates being thoroughly and skillfully riveted there remains the important matter of strengthening the boiler against the enormous internal pressure not altogether provided for.

Fig. 42.

To illustrate the importance of attention to this point it may be remarked that a boiler eighteen feet in length by five feet in diameter, with 40 four-inch tubes, under a head of 80 pounds of steam, has a pressure of nearly 113 tons on each head, 1,625 tons on the shell and 4,333 tons on the tubes, making a total of 6,184 tons on the whole of the exposed surfaces.

Not only is this immense force to be withstood, but owing to the fact that the boiler grows weak with age—a safety factor of six has been adopted by inspectors, i.e., the boiler must be made six times as strong as needed in every day working practice.

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Fig. 43.

Braces in the Boiler.—The proper bracing of flat surfaces exposed to pressure, is a matter of the greatest importance, as the power of resistance to bulging possessed by any considerable extent of such a surface, made as they must be in the majority of cases of thin plates, is so small that practically the whole load has to be carried by the braces. This being the case, it is evident that as much attention should be given to properly designing, proportioning, distributing and constructing the brace as to any other portion of the boiler.

All flat surfaces should be strongly supported with braces of the best refined iron, or mild steel, having a tensile strength of not less than 58,000 lbs. to the square inch. These braces must be provided with crow feet or heavy angle iron properly distributed throughout the boiler.

Fig. 44.

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Fig. 42 shows the method usually followed in staying small horizontal tubular boilers. The cut represents a 36-inch head and there are five braces in each head: two short ones and three long ones. The braces should be attached to shell and head by two rivets at each end. The rivets should be of such size that the combined area of their shanks will be at least equal to the body of the brace, and their length should be sufficient to give a good large head on the outside to realize strength equal to the body of the brace.

In boilers with larger diameters, 5 to 8 feet, stay ends are made of angle or T iron; by this arrangement the stays can be placed further apart, the angle irons very effectively staying the plate between the stays, and thus affording more room in the body of the boiler. The size of the stays have to be increased in proportion to the greater load they have to sustain. See Fig. 43.

In a 66-inch boiler it is proper to have not less than 10 braces in each head, none under three feet in length, made of the best round iron one inch in diameter, with ends of braces made of iron 2¹⁄₂ × ¹⁄₂ inches with three pieces of T iron riveted to head above the tubes to which the braces are attached with suitable pins or turned bolts. See Fig. 44.

Staying of Flat Surfaces.—When boilers are formed principally of flat plates, like low-pressure marine boilers, or the fire-boxes of locomotive boilers, the form contributes nothing to the strength, which must, therefore, be provided for by staying the opposite furnaces together. Fig. 45 shows the arrangement of the stays in a locomotive fire-box. They are usually pitched about 4 inches from centre to centre, and are fastened into the opposite plates by screwing, as shown, the heads being riveted over. Each stay has to bear the pressure of steam on a square aa, and the sectional area of the stay must be so chosen that the tensile strength will be sufficient to bear the strain with the proper factor of safety.

Fig. 45.

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If the spaces between the stays are too great, or the plate too thin, there is a danger of the structure yielding through the plate bulging outwards between the points of attachment of the stays, thus allowing the latter to draw through the screwed holes made in the plates.

In designing boilers with stayed surfaces, care should be taken that the opposite plates connected by any system of stays should, as far as possible, be of equal area, otherwise there is sure to be an unequal distribution of load in the stays, some receiving more than their proper share, and moreover, the least supported plate is exposed to the danger of buckling.

Rule for Finding Pressure or Strain on Bolts.

The absolute stress or strain on a flat surface of a steam boiler, which is carried by the stays, can be easily determined by a simple rule:

Choose 3 stays as A B C in Fig. 46, measure from A to B in inches, and from A to C. Multiply these two numbers together and the result is the number of square inches of surface depending upon one bolt for supporting strength.

Example.

Suppose the stays measure from center to center 5 inches each way with steam at 80 lbs., then

5 × 5 = 25 × 80 = 2,000 lbs. borne by 1 stay.

Note.

The pressure on the surface does not include the space occupied by the area of the stay bolt, hence, to be absolutely correct that must be deducted.

Fig. 46.

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GUSSET STAYS.

The flat ends of cylindrical boilers are, especially in marine boilers, stayed to the round portions of triangular plates of iron called gusset stays. These are simply pieces of plate iron secured to the boiler front or back, near the top or bottom, by means of two pieces of angle iron, then carried to the shell plating, and again secured by other pieces of angle bar. This arrangement is shown in Fig. 47.

Fig. 47.

Palm Stays.—These are shown in Fig. 48, and are often used in the same position as a gusset stay; that is, from the back or front end of the boiler to the shell plates; they are sometimes used to stay the curved tops of combustion chambers.

Fig. 48.

The two opposite ends are also stayed together by long bar stays, running the whole length of the boiler, it is dangerous, however, to trust too much to the latter class of stays; for, in consequence of the alternate expansion and contraction which101 takes place every time the boiler is heated and cooled, they have a tendency to work loose at the joints; and if the portion of the boiler in which they are situated should happen to be hotter than the outside shell, they have a tendency to droop and are then perfectly useless.

RIVETED OR SCREW STAYS.

Fig. 49.

In addition to palm and gusset stays, there are in use riveted or screwed stays, as shown in Fig. 49.

This would not answer in furnaces, owing to the burning off of the heads, hence driven stays are used there.

Fig. 50.

These screwed stays, shown in Fig. 50, are used (in marine and similar boilers) between the combustion chamber back and boiler back and also between the sides of the combustion chambers.

The general plan is to have a large nut and washer inside and outside the boiler with the outside washer considerably larger than the inside, so as to hold more efficiently the back and front ends together.

In marine boilers it is customary to place the stays 15 to 18 inches apart for ease of access to the parts of the boiler, and to make them of 2¹⁄₄ to 2¹⁄₂ inch iron of the best quality.

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INSPECTOR’S RULES RELATING TO BRACES IN STEAM BOILERS, ALSO TO BE OBSERVED BY ENGINEERS.

Where flat surfaces exist, the inspector must satisfy himself that the spacing and distance apart of the bracing, and all other parts of the boiler, are so arranged that all will be of not less strength than the shell, and he must also after applying the hydrostatic test, thoroughly examine every part of the boiler.

No braces or stays employed in the construction of marine boilers shall be allowed a greater strain than six thousand pounds per square inch of section, and no screw stay bolt shall be allowed to be used in the construction of marine boilers in which salt water is used to generate steam, unless said stay bolt is protected by a socket. But such screw stay bolts, without sockets, may be used in staying the fire boxes and furnaces of such boiler, and not elsewhere, when fresh water is used for generating steam in said boiler. Water used from a surface condenser shall be deemed fresh water. And no brace or stay bolt used in a marine boiler will be allowed to be placed more than eight and one-half inches from centre to centre, except that flat surfaces, other than those on fire boxes, furnaces and back connections, may be reinforced by a washer or T iron of such size and thickness as would not leave such flat surface unsupported at a greater distance, in any case, than eight and one-half inches, and such flat surface shall not be of less strength than the shell of the boiler, and able to resist the same strain and pressure to the square inch, and no braces supporting such flat reinforced surfaces, will be allowed more than 16 inches apart.

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In allowing the strain on a screw stay bolt, the diameter of the same shall be determined by the diameter at the bottom of the thread. Many State laws and City ordinances allow a strain of seven thousand five hundred pounds per square inch of section on good bracing without welds. The following table gives the safe load of round iron braces or stays.

DIAMETER OF BRACE.

Shop Names for Boiler Braces.—1. Gusset brace (fig. 47). 2. Crowfoot brace. 3. Jaw brace (fig. 44). 4. Head to head brace (fig.50). These shop terms refer to braces used in the tubular form of boiler.

A Stay and a Brace in a steam boiler fulfil the same office, that of withstanding the pressure exerted outward of the expanded and elastic steam.

Socket Bolts are frequently used instead of the screw stay between the inside and outside plates that form the centre space. Socket bolts are driven hot the same as rivets.

The method of bracing with T bars is considered the best; the bars make the flat surface rigid and unyielding even before the brace is applied. The braces should be spaced about 8 inches apart on the T bar and 7 inches from the edge of the flange T the bar should be 4″ × 4¹⁄₂″ T iron and riveted to the head or flat surface with ¹¹⁄₁₆″ rivets spaced 4¹⁄₂ inches apart.

Hollow Stay Bolts are used in locomotive fire boxes to show when fracture has occurred by permitting an escape of steam or water.

The flange of a boiler head ¹⁄₂″ thick will amply support 6 inches from the edge of the flange.

A radius of 2 inches is ample for bend of flange on the head. The lower braces should be started 6 inches above the top row of tubes. Braces should be fitted so as to have a straight pull, i.e. parallel with the boiler shell. The heads of the boiler should be perfectly straight before the braces are fitted in place. Gusset brace plates should not be less than 30 inches long and 14 inches wide. Braces are best made of 1 inch O iron of highest efficacy with tensile strength of not less than 58,000 lbs. to the square inch.

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Fig. 51.

The riveted stay shown in Fig. 51, consists of a long rivet, passed through a thimble or distance piece of wrought iron pipe placed between plates, to be stayed together, and then riveted over in the usual manner.

An ingenious device is in use to show when a bolt has broken. A small hole is drilled into the head, extending a little way beyond the plate, and as experience shows that the fracture nearly always occurs next to the outside plate, that is the end taken for the bored out head: when the bolt is broken the rush of steam through the small hole shows the danger without causing serious disturbance.

Even where the best of iron is used for stay bolts they should never be exposed to more than ¹⁄₁₀th or ¹⁄₁₂th their breaking strength.

The stays should be well fitted, and each one carefully tightened, and, as far as possible each stay in a group should have the same regular strain upon it—if the “pull” all should come on one the whole are liable to give way.

Dimensions and Shape of Angle and T Iron.

Fig. 52.

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The condition of a boiler can be learned by tapping on the sheets, rivets, seams, etc., to ascertain whether there are any broken stays, laminated places, broken rivets, etc.

Fig. A.

Fig. B.

Fig. A represents the method of preparing testing pieces of boiler plate, for the machines prepared specially to measure their elongation before breaking, and also the number of pounds they will bear stretching before giving way. Fig. B exhibits the same with reference to the brace and other O iron.

RULES AND TABLES
FOR DETERMINING AREAS AND CALCULATING THE CONTENTS OF STEAM AND WATER SPACES IN THE STEAM BOILER.

In order to ascertain the number of braces, which are necessary to strengthen that part of the boiler head, which is not stayed by the tubes, it is first necessary to know its area; the part to be stayed is a segment of a circle.

The length of the segment is measured above the top row of the tubes, and its height or width is equal to the distance from the top of the tubes to the top of the boiler shell.

Since, however, part of this segment is braced by the boiler shell, and also by the top row of the tubes, it has been generally agreed that the length of the segment should be measured two inches above the tubes, and the height or width, should be measured from a line, drawn two inches above the tubes, to a point within three inches from the top of the boiler shell, as106 shown in the illustration by the dotted line. Thus, referring to Fig. D, the length of the segment is equal to l, and the height is equal to h.

Rule. The area of a segment may be obtained, very approximately, by dividing the cube of the width (or height) by twice the length of the chord, and adding to the quotient the product of the width into two-thirds of the chord.

Example. If we suppose the height h of the segment in Fig. D to be equal to 18 inches, and the length l to be equal to 48 inches, we have

18³ ÷ (48 × 2) + (48 × ²⁄₃ × 18) = 60.7 + 576.0 = 636.7 square inches.

Fig. C.Fig. D.

In order to calculate the contents of the steam and water spaces of a boiler, the same rule, as above, may be employed. The volume of the steam space may be readily obtained by the above rule, taking the distance from the water level to the top of the shell for the height, and the diameter of the shell, measured at the water line, for the length of the segment lines.

The area of the segment thus found, expressed in square inches, divided by 144, and multiplied by the length of the boiler in feet, is equal to the steam space, in cubic feet, this result is slightly reduced by the space occupied by the braces.

In order to find the volume of the water space, it is first necessary to find the total area of the boiler head, and this107 minus the area of the segment above the water line, is equal to the area of the segment below the water line. From this must also be subtracted the combined cross sectional area of the tubes.

Thus, the rule for finding the volume of the steam space in cubic feet.

1. Find the area of the segment of the boiler head, above the water line, in square inches.

2. Divide this by 144, and multiply the quotient by the length of the boiler in feet.

To find the volume of the waterspace in cubic feet.

1. Find the area of the boiler head in square inches.

2. Multiply the square of the outside diameter of one tube by .7854, and multiply this by the number of tubes, and add to the product, the area of the segment above the waterline.

3. Subtract 2 from 1, and divide the remainder by 144.

4. Multiply the quotient by the length of the boiler in feet.

To find the number of braces, necessary for the flat surface above the tubes.

1. Find the area of the segment of the boiler head, which is to be braced, in square inches.

2. Multiply the area, thus found, by the steam pressure in pounds per square inch.

3. Multiply the cross sectional area of one brace by the number of pounds, which it is allowed to carry, per square inch of section.

4. Divide product 2 by product 3, and the result is the number of braces, required for the head.

Table No. 1 gives the total area in square inches. No. 2, areas to be braced. No. 3, number of braces of one inch round iron required, allowing seven thousand five hundred pounds per square inch of section at one hundred pounds steam pressure.

Table No. 3 will be found of more practical use than Table 2, for it gives directly the number of braces required in any given boiler, instead of the area to be braced. It was calculated from Table 2. The iron used in braces will safely stand108 a continuous pull of 7,500 pounds to the square inch, which is the figure used in computing the foregoing table. A round brace an inch in diameter has a sectional area of .7854 of an inch, and the strain that it will safely withstand is found by multiplying .7854 by 7,500, which gives 5,890 pounds as the safe working strain on a brace of one-inch round iron.

In a 60-inch boiler, whose upper tubes are 28 inches below the shell, the area to be braced is, according to table 2, 930 square inches. If the pressure at which it is to be run is 100 pounds to the square inch, the entire pressure on the area to be braced will be 93,000 pounds, and this is the strain that must be withstood by the braces. As one brace of inch-round iron will safely stand 5,890 pounds, the boiler will need as many braces as 5,890 is contained in 93,000, which is 15.8. That is, 16 braces will be required. The table is made out on the basis of 100 lbs. pressure to the square inch, because that is a very convenient number.

Table No. 1. TOTAL AREA ABOVE TUBES OR FLUES.

(Square Inches.)

109

Table 2. AREAS TO BE BRACED. (Square Inches.)

Table 3. NUMBER OF BRACES REQUIRED, AT 100 LBS. PRESSURE.

110

In Table 2 this calculation has been made for all sizes of boilers that are ordinarily met with. The area to be braced has been calculated as above in each case, the two-inch strip above the tubes, and the three-inch strip around the shell being taken into account. As an example of its use, let us suppose that upon measuring a boiler we find that its diameter is 54 inches, and that the distance from the upper tubes to the top of the shell is 25 inches. Then by looking in the table under 54″ and opposite 25″ we find 714, which is the number of square inches that requires staying on each head.

BOILER TUBES.

Table.

Dimensions of Lap Welded Boiler Tubes.

The above is the regular manufactures’ list of sizes and weights.

Note.

Boiler tubes are listed and described from the outside diameter. This should be noted, as gas-pipe is described from the inside diameter. Thus a 1-inch gas-pipe is nearly 1¹⁄₄ outside diameter while a 1-inch boiler tube is exactly one inch. Another difference between the two consists in the fact that the outside of boiler tubes is rolled smooth and even; gas-pipe is left comparatively rough and uneven.

111

When the boiler tubes are new and properly expanded there is a large reserve or surplus of holding power for that part of the tube sheet supported by them, this has been proved by experiment made by chief engineer W. H. Stock, U. S. N., as shown in the following

Table of Holding Power of Boiler Tubes.

Mr. C. B. Richards, consulting engineer at Colt’s Armory at Hartford, Conn., made some experiments as to the holding power of tubes in steam boilers, with the following results: The tubes were 3 inches in external diameter, and 0.109 of an inch thick, simply expanded into a sheet ³⁄₈ of an inch thick by a Dudgeon expander. The greatest stress without the tubes yielding in the plate was 4,500 pounds, and at 5,000 pounds was drawn from the sheet. These experiments were repeated with the ends of the tubes which projected through the sheet three-sixteenths of an inch, being flared so that the external diameter in the sheet was expanded to 3.1 inches. The greatest stress without yielding was 18,500 pounds; at 19,000 pounds yielding was observed; and at 19,500 pounds it was drawn from the sheet. The force was applied parallel to the axis of the tube, and the sheet surfaces were held at right angles to the tube axis.

112

Note.

When the tube sheet and tube ends near the sheet become coated with scale or the tubes become overheated, the holding power of the tubes becomes largely reduced, and caution must be used in having the tube ends re-expanded and accumulated scale removed.

Note 2.—In considering the stress or strain upon the expanded or riveted over ends of a set of boiler tubes, it may be remembered that the strain to be provided against is only that coming upon tube plate, exposed to pressure, between the tube ends—the space occupied by the tubes has no strain upon it.

The gauge to be employed by inspectors to determine the thickness of boiler plates will be any standard American gauge furnished by the Treasury Department.

All samples intended to be tested on the Riehle, Fairbanks, Olson, or other reliable testing machine, must be prepared in form according to the following diagram, viz.: eight inches in length, two inches in width, cut out their centres as indicated.

Fig. E.

Portions of the Marine Boiler which Become Thin by Wear.

These are generally situated, 1st, at or a little above the line of fire bars in the furnace; 2d, the ash pits; 3d, combustion chamber backs; 4th, shell at water line; 5th, front and bottom of boiler.

The thinning can usually be detected by examination, sounding with a round nosed hammer, or drilling small holes in suspected parts not otherwise accessible for examination.

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EXAMPLES OF CONSTRUCTION AND DRAWING

The small table above is of use in this and the four succeeding pages; in all places in the drawings where “d” is used it indicates the diameter of the rivet; “t” means the thickness of the plate; “p” stands for pitch. The table also shows the proportion of rivet to the plate—thus, a ¹⁄₄-inch plate requires a ⁹⁄₁₆ rivet, etc.

It is recommended, in view of the increased disposition on the part of official examiners to test the applicant’s knowledge of drawing, for any one interested, to redraw to a full size all the rivets, plates, and methods of joining the two contained on pages 113-116.

Fig. 53.

Fig. 54.

The figures 53 to 60 will be understood without much explanation.

In figures 53 and 54 the cup head, the conical head and pan head rivets are shown.

Figs. 55 and 56 exhibit the details (and drawings) of single and double riveting. Where the cut reads p = (2¹⁄₂)d, it means that the distance from the centre of one rivet to the centre of the next shall be 2¹⁄₂ the diameter of the rivet, see example, page 115.

114

Fig. 55.

Fig. 56.

115

Example.

If the size of the rivet used is ⁷⁄₈ths, then ⁷⁄₈ × 2¹⁄₂ = 2²⁄₁₀ inches nearly, and this gives the proportionate strength of the plate and the rivet, see page 113.

Fig. 57.

Figs. 57, 58, 59 and 60 show quite clearly the joints and rivet work done in locomotive and marine work. Fig. 60 shows method of riveting 3 plates, A, B, and C, together.

116

Fig. 58.

Fig. 59.

Fig. 60.

117

RULE FOR SAFE INTERNAL PRESSURE

The safe internal pressure on cylindrical shells is found according to the following rule, which has been adopted by the United States Board of Supervising Inspectors, and any boiler shell not found in the tables can be determined by this rule.

Rule.—Multiply one-sixth of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thickness—expressed in inches or parts of an inch—of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter—also expressed in inches—and the result will be the pressure allowable per square inch of surface for single riveting, to which add twenty per centum for double riveting.

The hydrostatic pressure applied, under this table and rule, must be in the proportion of one hundred and fifty pounds to the square inch, to one hundred pounds to the square inch of the working pressure allowed.

Example.

What pressure should be allowed to be carried on a boiler 60″ diameter, made of plates ³⁄₈″ thick, having a tensile strength of 60,000 pounds? Now then:

6)60,000
———
 10,000
3
———
8)30,000
———
Half diam.    30)3750(125. lbs.—if single riveted.
30
——
75
60
——
150      125 + 25 lbs. (20 feet) = 150 for
150          double riveted.

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TABLES SAFE INTERNAL PRESSURE.

121

DEFINITION OF TERMS.

In the accompanying sections, some of the properties of iron and steel, as employed in the construction of boilers, are given. It is, therefore, desirable that the meanings applied to the various terms used should be clearly understood. The definitions necessary are, then, briefly as follows:—

Tensile strength is equivalent to the amount of force which, steadily and slowly applied in a line with the axis of the test piece, just overcomes the cohesion of the particles, and pulls it into separate parts.

Contraction of area is the amount by which the area, at the point where the specimen has broken, is reduced below what it was before any strain or pulling force was applied.

Elongation is the amount to which the specimen stretches, between two fixed points, due to a steady and slowly applied force, which pulls and separates it into parts. Elongation is made up of two parts: one due to the general stretch, more or less, over the length; the other, due to contraction of area at about the point of fracture.

Shearing strength is equivalent to the force which, if steadily and slowly applied at right angles, or nearly so, to the line of axis of the rivet, causes it to separate into parts, which slide over each other, the planes of the surface at the point of separation being at right angles, or nearly so, to the axis of the rivet.

Elastic limit is the point where the addition to the permanent set produced by each equal increment of load or force, steadily and slowly applied, ceases to be fairly uniform, and is suddenly, after the point is reached, increased in amount. It is expressed as a percentage of the tensile strength.

Tough.—The material is said to be “tough” when it can be bent first in one direction, then in the other, without fracturing. The greater the angles it bends through (coupled with the number of times it bends), the tougher it is.

Ductile.—The material is “ductile” when it can be extended by a pulling or tensile force and remain extended after the force is removed. The greater the permanent extension, the more ductile the material.

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Elasticity is that quality in a material by which, after being stretched or compressed by force, it apparently regains its original dimensions when the force is removed.

Fatigued is a term applied to the material when it has lost in some degree its power of resistance to fracture, due to the repeated application of forces, more particularly when the forces or strains have varied considerable in amount.

Malleable is a term applied to the material when it can be extended by hammering, rolling, or otherwise, without fracturing, and remains extended. The more it can be extended without being fractured, the more malleable it is.

Weldable is a term applied to the material if it can be united, when hot, by hammering or pressing together the heated parts. The nearer the properties of the material, after being welded, are to what they were before being heated and welded, the more weldable it is.

Cold-short is a name given to the material when it cannot be worked under the hammer or by rolling, or be bent when cold without cracking at the edges. Such a material may be worked or bent when at a great heat, but not at any temperature which is lower than about that assigned to dull red.

Hot-short is when the material cannot be easily worked under the hammer, or by rolling at a red-heat at any temperature which is higher than about that assigned to a red-heat, without fracturing or cracking. Such a material may be worked or bent at a less heat.

Homogeneous describes a material which is all of the same structure and nature.

A homogeneous material is the best for boilers, and it should be of suitable tensile strength with contraction of area and elongation best suited for the purpose, having an elastic limit that will insure the structure being reliable; it should be tough and ductile, and its elasticity fairly good, and be capable of enduring strains without becoming too quickly or easily fatigued. The material should be malleable and in some cases weldable; that which is of a decidedly cold-short or hot-short nature should be avoided.

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BOILER REPAIRS.

Fig. 66.

This cut represents a form of clamp used in holding the plates against each other when being riveted.

Fig. 67.

REPAIRING CRACKS.

Cracks in the crown-sheet or side of a fire-box boiler, or top head of the upright boiler can be temporarily repaired by a row of holes drilled and tapped touching one another, with ³⁄₈ or ¹⁄₂ inch copper plugs or bolts, screwed into the plates and afterwards all hammered together.

For a permanent job, cut out the defect and rivet on a patch. This had better be put on the inside, so as to avoid a “pocket” for holding the dirt. In putting on all patches, the defective part must be entirely removed to the solid iron, especially when exposed to the fire.

Note.—When fire comes to two surfaces of any considerable extent, the plate next to the fire becomes red-hot and weakens, hence the inside plate, in repairs, must be removed.

The application of steel patches to iron boilers is injudicious. Steel and iron differ structurally and in every other particular, and their expansion and contraction under the influence of changing temperatures, is such that trouble is sure to result from their combination.

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DEFECTS AND NECESSARY REPAIRS.

Fig. 68.

Fig. 68 represents a patch called a “spectacle piece.” This is used to repair a crack situated between the tube ends. These are usually caused (if the metal is not of bad quality) by allowing incrustation to collect on the plate inside the boiler, or by opening the furnace and smoke doors, thus allowing a current of cold air to contract the metal of the plates round the heated and expanded tubes.

The “spectacle piece” is bored out to encircle the tubes adjacent to the crack, or in other words, to be a duplicate of a portion of the tube plate cracked. These plates are then pinned on to the tube covering the crack.

Steam generators, as they are exposed to more or less of trying service in steam production, develop almost an unending number and variety of defects.

When a boiler is new and first set up it is supposed to be clean, inside and out, but even one day’s service changes its condition; sediment has collected within and soot and ashes without.

Unlike animals and plants they have no recuperative powers of their own—whenever they become weakened at any point the natural course of the defect is to become continually worse.

In nothing can an engineer better show his true fitness than in the treatment of the beginnings of defects as they show themselves by well-known signs of distress, such as leaks of water about the tube ends, and in the boiler below the water line, or escaping steam above it. In more serious cases, the professional services of a skillful and honest boiler maker is the best for the occasion.

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In a recent report given in by the Inspectors the following list of defects in boilers coming under their observation was reported. The items indicate the nature of the natural decay to which steam boilers in active use are exposed. The added column under the heading of “dangerous” carries its own lesson, urging the importance of vigilance and skill on the part of the engineer in charge.

This list covers nearly, if not all, the points of danger against which the vigilance of both engineer and fireman should be continually on guard; and is worth constant study until thoroughly memorized.

Note.

Probably one-quarter, if not one-third, of all boiler-work is done in the way of repairs, hence the advice of men who have had long experience in the trade is the one safe thing to follow for the avoidance of danger and greater losses, and for the best results the united opinion of 1, the engineer, experienced in his own boiler and 2, the boiler-maker with his wider observation and 3, the owner of the steam plant, all of whom are most interested.

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Corrosion is a trouble from which few if any boilers escape. The principal causes of external corrosion arise from undue exposure to the weather, improper setting, or possibly damp brick work, leakage consequent upon faulty construction, or negligence on the part of those having them in charge.

Internal corrosion maybe divided into ordinary corroding, or rusting and pitting. Ordinary corrosion is sometimes uniform through a large portion of the boiler, but is often found in isolated patches which have been difficult to account for. Pitting is still more capricious in the location of its attack; it may be described as a series of holes often running into each other in lines and patches, eaten into the surface of the iron to a depth sometimes of one-quarter of an inch. Pitting is the more dangerous form of corrosion, and the dangers are increased when its existence is hidden beneath a coating of scale. There is another form of decay in boilers known as grooving; it may be described as surface cracking of iron, caused by its expansion and contraction, under the influence of differing temperatures. It is attributable generally to the too great rigidity of the parts of the boiler affected, and it may be looked upon as resulting from faulty construction.

Fig. 69.

In plugging a leaky tube with a pine plug, make a small hole, of ³⁄₁₆ of an inch diameter, or less, running through it from end to end. These plugs should never have a taper of more than ¹⁄₈ of an inch to the foot. It is well to have a few plugs always on hand. Fig. 69 exhibits the best shape for the wooden plug.

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QUESTIONS
BY THE PROPRIETOR TO THE ENGINEER IN CHARGE, RELATING TO CONDITION OF THE BOILER,

How long since you were inside your boiler?

Were any of the braces slack?

Were any of the pins out of the braces?

Did all the braces ring alike?

Did not some of them sound like a fiddle-string?

Did you notice any scale on flues or crown sheet?

If you did, when do you intend to remove it?

Have you noticed any evidence of bulging in the fire-box plates?

Do you know of any leaky socket bolts?

Are any of the flange joints leaking?

Will your safety-valve blow off itself, or does it stick a little sometimes?

Are there any globe valves between the safety-valve and the boiler? They should be taken out at once, if there are.

Are there any defective plates anywhere about your boiler?

Is the boiler so set that you can inspect every part of it when necessary?

If not, how can you tell in what condition the plates are?

Are not some of the lower courses of tubes or flues in your boiler choked with soot or ashes?

Do you absolutely know, of your own knowledge, that your boiler is in safe and economical working order, or do you merely suppose it is?

QUESTIONS
ASKED OF A CANDIDATE FOR A MARINE LICENSE RELATING TO DEFECTS IN BOILER WITH ANSWERS.

If you find a thin plate, what would you do?
Put a patch on.

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Would you put it on inside or outside?
Inside.

Why so?
Because the action that has weakened the plate will then act on the patch, and when this is worn it can be replaced; but the plate remains as we found it.

If the patch were put on the outside, the action would still be on the plate, which would in time be worn through, then the pressure of the steam would force the water between the plate and the patch, and so corrode it; and during a jerk or extra pressure, the patch might be blown off.

It is on the same principle that mud-hole doors are on the inside.

If you found several thin places, what would you do?
Patch each, and reduce the pressure.

If you found a blistered plate?
Put a patch on the fire side.

If you found a plate at the bottom buckled?
Put a stay through the centre of the buckle.

If you found several?
Stay each, and reduce the pressure.

The crown of the furnace down?
Put a stay through the middle, and a dog across the top.

If a length of the crown were down, put a series of stays and dogs.

A cracked plate?
Drill a hole at each end of the crack; caulk the crack, or put a patch over it.

If the water in the boiler is suffered to get too low, what may be the consequence?
Burn the top of the combustion chamber and the tubes; perhaps cause an explosion.

If suffered to get too high?
Cause priming; perhaps cause the breaking of the cylinder covers.

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THE INSPECTION OF STEAM BOILERS.

Let it be clearly understood that if there were no steam generators using steam under pressure there would he no boiler inspection, and no licensing of engineers; it requires no license to be a machinist or a machine tender, no more would a license be essential to run a steam engine, except it were connected with the boiler. The danger to the public arising from their use requires that the care and management of high-pressure steam boilers shall be in hands of careful, experienced and naturally ingenious men, hence it is on the affairs of the Boiler Room that the first tests are made, as to the worthiness of an aspirant for an engineer’s license, hence, too, the success of many firemen in obtaining the preference over engine-builders or school graduates, in the line of promotion as steam engineers.

The inspection laws of the various states and cities are framed after substantially the same leading ideas, and in presenting one the others may be assumed to be nearly the same.

The special province of the Steam Boiler Inspection and Engineers’ Bureau in the police department in New York City is to inspect and test all the steam boilers in the city, at certain stated periods, and to examine every applicant for the position of engineer as to his ability and qualifications for running an engine and boiler with safety.

According to the laws of the State, every owner, agent or lessee, of a steam boiler or boilers, in the city of New York, shall annually report to the board of police, the location of said boiler or boilers, and, thereupon, the officers in command of the sanitary company shall detail a practical engineer, who shall proceed to inspect such steam boiler or boilers, and all apparatus and appliances connected therewith.

When a notice is received from any owner or agent that he has one or more boilers for inspection, a printed blank is returned to him stating that on the day named therein the boilers130 will be tested, and he is asked to make full preparation for the inspection by complying with the following rules:

Be ready to test at the above-named time.
Have boiler filled with water to safety-valve.
Have 1¹⁄₄-inch connection.
Have steam gauge.
Steam allowed two-thirds amount of hydrostatic pressure.

More particularly stated, the following have been adopted by one or more Inspection Companies:

How to Prepare for Steam-Boiler Inspection.

1. Haul fires and all ashes from furnaces and ash pits.

2. If time will permit, allow boiler and settings to cool gradually until there is no steam pressure, then allow water to run out of boilers. It is best that steam pressure should not exceed ten pounds if used to blow water out.

3. Inside of boiler should be washed and dried through manholes and handholes by hose service and wiping.

4. Keep safety-valves and gauge-cocks open.

5. Take off manhole and handhole plates as soon as possible after steam is out of boiler, that boiler may cool inside sufficiently for examination; also keep all doors shut about boilers and settings, except the furnace and ash-pit doors. Keep dampers open in pipes and chimneys.

6. Have all ashes removed from under boilers, and fire surfaces of shell and heads swept clean.

7. Have spare packing ready for use on manhole and handhole plates, if the old packing is made useless in taking off or is burned. The boiler attendant is to take off and replace these plates.

8. Keep all windows and doors to boiler room open, after fires are hauled, so that boilers and settings may cool as quickly as possible.

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9. Particular attention is called to Rule 5, respecting doors—which should be open and which closed—also arrangement of damper. The importance of cooling the inside of the boiler by removal of manhole and handhole plates at the same time the outside is cooling, is in equalizing the process of contraction.

ISSUING CERTIFICATES.

These conditions having been complied with, the boiler is thoroughly tested, and if it is deemed capable of doing the work required of it, a number by which it shall hereafter be known and designated is placed upon it in accordance with the city ordinance: Failure to comply with this provision is punishable by a fine of $25. A certificate of inspection is then given to the owner, for which a fee of $2 is paid.

This certificate sets forth that on the day named the boiler therein described was subject to a hydrostatic pressure of a certain number of pounds to the square inch. The certificate tells where the boiler was built, its style or character and “now appears to be in good condition and safe to sustain a working pressure of —— to the square inch. The safety-valve has been set to said pressure.” A duplicate of this certificate is posted in full view in the boiler-room. In case the boiler does not stand the test to which it is subject, it must be immediately repaired and put in good working order before a certificate will be issued.

THE HYDRAULIC TEST.

The hydraulic test is a very convenient method of testing the tightness of the work in a new boiler, in conjunction with inspection to a greater or lesser degree, in the passing of new work. As a detector of leakages it has no rival, and its application enables faulty caulking to be made good before the boiler has left the works, and before a leak has time to enter on its insidious career of corrosion. The extent to which it enables the soundness and quality of the work to be ascertained is another matter, and depends on several conditions. It will be evident that if the test be applied with this object to a new boiler, the pressure should range to some point in excess of the132 working load if such a test is to be of any practical value.

What the excess should be so as to remain within safe limits cannot be stated without regard being paid to the factor of safety adopted in the structure.

In addition to the advantage which the hydraulic test affords as a means of proving the tightness of the riveted seams and work generally, it is also of frequent assistance in determining the sufficiency of the staying of flat surfaces, especially when of indeterminate shape, or when the stresses thrown upon them by the peculiar construction of the boiler are of uncertain magnitude. For the hydraulic test, however, to be of any real value in the special cases to which we refer, it is essential that it should be conducted by an expert, and the application of the pressure accompanied by careful gaugings, so as to enable the amount of bulging and permanent set to be ascertained. Without such readings the application of the test in such cases is worthless, and may be delusive. Indeed, the careful gauging of a boiler as a record of its behavior should be a condition of every test, and is a duty requiring for its adequate performance a skilled inspector.

The duty of inspecting a new boiler or witnessing the hydraulic test properly belongs to one of the regular inspecting companies, who have men in their employ specially trained for the performance of such work. The advantage accruing from such a course is well worth the fee charged for the service, and secures a searching inspection of the workmanship, which frequently brings to light defects and oversights that a mere pumping-up of the boiler would never reveal. Such a proceeding in fact, can only prove that the boiler is water-tight, and a boiler may be tight under test although the workmanship is of the poorest character. Besides, it is well to bear in mind that the tightness of a boiler under test is no guarantee of its tightness after it is got to work. In a word, as far as new boilers are concerned, the application of hydraulic pressure unaccompanied by careful inspection and gaugings may be almost worthless, while with these additions it may be extremely valuable, especially in the case of boilers of peculiar shape, and is a precaution that should not be neglected.

133

ENGINEERS’ EXAMINATIONS.

Keeping in mind the fact that if there were no steam-boilers there would be no examinations and no public necessity for licenses, these “points” are added.

Examinations are trying periods with all engineers, as the best are liable to fail in their answers from a nervous dread of the ordeal, but the granting of the document is very largely influenced by the personal experience of the candidate in the practical duties of the engine and boiler-room, which must be stated and certified to by the evidence of others.

A general knowledge of the subject of steam engineering is the first requisite to success. A few sample questions are here given to show the ordinary course pursued by examiners to determine the fitness of applicants:

134

MECHANICAL STOKERS.

In the back counties of England for many generations before the steam engine was evolved from the brains of Trevithick, Watt and Stephenson, the word “stoke” was used, meaning to “stir the fire.” The word was derived from an ancient word, stoke, meaning a stick, stock or post.

To-day there are very many men who are called “stokers,” employed principally on locomotive engines, steam vessels, etc., and then there is the “stoke hole,” so-called, in which they do their work.

But, now comes the “mechanical stoker,” which is well named, as its office is to feed and “stir the fire” by a machine, thus relieving the fireman from much excessively hard toil and allowing the time and energy thus saved to be more profitably used elsewhere. The figure shows a view of the American Stoker which is a device of the most advanced type.

The principal parts of the machine are: 1, the Hopper, which may be filled either by hand shoveling or by elevating and conveying machinery; 2, the Conveyor Screw, which forces the coal, or indeed, any description of fuel, forward to the 3, Magazine, shown in the figure to the left; 4, a Driving Mechanism, which is a steam motor arranged conveniently in front of the hopper; 5, the Retort, so called from its being the place (above the conveyor) where the coal is distilled into gas.

Note.—An illustrated printed description of this machine is issued and sent free upon application by the makers. The American Stoker Co., Washington Life Building, Cor. Broadway and Liberty St., New York.

135

The rate of feeding coal is controlled by the speed of the motor, this being effected by the simple means of throttling the steam in the supply pipe to the motor. The shields covering the motor effectually protect the mechanism from dirt and dust. The motor has a simple reciprocating piston; its piston rod carries a crosshead, which, by means of suitable connecting links, operates a rocker arm having a pawl mechanism, which in turn actuates the ratchet wheel attached to the conveyor shaft. The stoker is thus entirely self-contained and complete in itself.

A screw conveyor or worm is located in the conveyor pipe and extends the entire length of the magazine. Immediately beneath the conveyor pipe is located the wind-box, having an opening beneath the hopper.

At this point is connected the piping for the air supply, furnished at low pressure by a volume blower. The other end of the wind-box opens into the air space between the magazine and outer casing. The upper edge of the magazine is surrounded by tuyeres, or air blocks, these being provided with openings for the discharge of air, inwardly and outwardly.

The stoker rests on the front and rear bearing bars; the space between the sides of the stoker and side walls is filled with iron plates, termed “dead grates.” Steam is carried to the motor by a ³⁄₄-inch steam pipe. The exhaust steam from the motor is discharged into the ash pit.

In operation the coal is fed into the hopper, carried by the conveyor into the magazine, which it fills, “overflows” on both sides, and spreads upon the sides of the grates. The coal is fed slowly and continuously, and, approaching the fire in its upward course, it is slowly roasted and coked, and the gases released from it are taken up by the fresh air entering through the tuyeres, which explodes these gases and delivers the coal as coke on the grates above. The continuous feeding gives a breathing motion to this coke bed, thus keeping it open and free for the circulation of air.

It will be noted that in this machine the fuel is introduced from the bottom of the bed of fuel, technically speaking, upon the principle of “underfeeding.”

136

CHEMICAL TERMS

AND EXPLANATIONS RELATING TO FEED WATERS.

Chemistry is a science which investigates the composition and properties of material substances.

Nature is composed of elementary elements; knowledge of these bodies, of their mutual combinations, of the forces by which these combinations are brought about, and the laws in accordance with which these forces act, constitute chemistry, and the chemistry of steam engineering largely deals with the foreign bodies contained in the feed water of steam boilers.

Element. In general, the word element is applied to any substance which has as yet never been decomposed into constituents or transmuted to any other substance, and which differs in some essential property from every other known body. The term simple or undecomposed substance is often used synonymously with element.

There are about 70 simple elements, three-quarters of which are to be met with only in minute quantities and are called rare elements. Copper, silver, gold, iron, and sulphur are simple elements— the metal irridium, for example, is a rare element—it is the metal which tips the ends of gold pens—it is heavier than gold and much more valuable. Probably there are not two tons of it in existence.

A Re-agent is a chemical used to investigate the qualities of some other chemical—example, hydrochloric acid is a re-agent in finding carbonic acid in limestone, or carbonate of lime, which when treated by it will give up its free carbonic acid gas, which is the same as the gas in soda water.

An Oxide is any element, such as iron, aluminium, lime, magnesia, etc., combined with oxygen. To be an oxide it must pass through the state of oxidization. Iron after it is rusted is the oxide of iron, etc.

A Carbonate is an element, such as iron, sodium, etc., which forms a union with carbonic acid—the latter is a mixture of carbon and oxygen in the proportion of 1 part of carbon to 2 of oxygen. Carbonic acid, as is well known, does not support combustion and is one of the gases which come from perfect137 combustion. This acid, or what may be better termed a gas, is plentifully distributed by nature and is found principally combined with lime and magnesia, and in this state (i.e., carbonate of lime and carbonate of magnesia) is one of the worst enemies to a boiler.

An Acid is a liquid which contains both hydrogen and oxygen combined with some simple element such as chlorine, sulphur, etc. It will always turn blue litmus red, and has that peculiar taste known as acidity; acids range in their power from the corrosive oil of vitriol to the pleasant picric acid which gives its flavor to fruits.

Alkalies are the opposite to an acid; they are principally potash, soda and ammonia—these combined with carbonic acid form carbonates. Sal-soda is carbonate of soda.

A Chloride is an element combined with hydro chloric acid—common salt is a good example of a chloride—being sodium united with the element chlorine, which is the basis of hydro chloric acid. Chlorides are not abundant in nature but all waters contain traces of them more or less and they are not particularly dangerous to a boiler.

Sulphates are formed by the action of sulphuric acid (commercially known as the oil of vitriol) upon an element, such as sodium, magnesia, etc. The union of sodium and sulphuric acid is the well-known Glauber salts—this is nothing more than sulphate of soda; sulphate of lime is nothing more than gypsum. Sulphates are dangerous to boilers, if in large quantities should they give up their free acid—the action of the latter being to corrode the metal.

Silica is the gritty part of sand—it is also the basis of all fibrous vegetable matter—a familiar example of this is the ash which shows in packing, which has been burnt by the heat in steam; by a peculiar chemical treatment silica has been made into soluble glass—a liquid. 65 per cent. of the earth’s crust is composed of silica—it is the principal part of rock—pure white sand is silica itself—it is composed of an element called silicum combined with the oxygen of the air. Owing to its abundance in nature and its peculiar solubility it is found largely in all waters that come from the earth and is present in all boiler scale.

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In water analysis the term insoluble matter, is silica. This is one of the least dangerous of all the impurities that are in feed water.

Magnesia is a fine, light, white powder, having neither taste nor smell, almost insoluble in boiling, but less so in cold water. Magnesia as found in feed water exists in two states, oxide and a carbonate, when in the latter form and free from the traces of iron, tends to give the yellow coloring matter to scale—in R. R. work, yellow scale is called magnesia scale.

Carbonate of Magnesia is somewhat more soluble in cold than in hot water, but still requires to dissolve it 9,000 parts of the latter and 2,493 of former.

Magnesia, in combination with silica, enters largely into the composition of many rocks and minerals, such as soapstone, asbestos, etc.

Lime, whose chemical name is calcium, is a white alkaline earthy powder obtained from the native carbonates of lime, such as the different calcerous stones and sea shells, by driving off the carbonic acid in the process of calcination or burning.

Lime is procured on a large scale by burning the stone in furnaces called kilns, either mixed with the fuel or exposed to the heated air and flames that proceed from side fires through the central cavity of the furnace in which the stones are collected.

The calcined stones may retain their original form or crumble in part to powder; if protected from air and moisture they can afterwards be preserved without change.

Soda is a grayish white solid, fusing at a red heat, volatile with difficulty, and having an intense affinity for water, with which it combines with great evolution of heat.

The only reagent which is available for distinguishing its salts from those of the other alkalies is a solution of antimoniate of potash, which gives a white precipitate even in diluted solutions.

Sodium is the metallic base of soda. It is silver white with a high lustre; crystallizes in cubes; of the consistence of wax at ordinary temperatures, and completely liquid at 194°, and139 volatilizes at a bright red heat. It is very generally diffused throughout nature though apparently somewhat less abundantly than potassium in the solid crust of the globe.

Salt, the chloride of sodium, a natural compound of one atom of chloride and one of sodium. It occurs as a rock inter-stratified with marl, and sandstones, and gypsum, and as an element of salt springs, sea water, and salt water lakes.

The proportions of its elements are 60.4 per cent. of chlorine and 39.6 per cent. of sodium.

In salt made of sea water the salts of magnesia with a little sulphate of lime are the principal impurities.

The above mentioned chemical substances can be classified into two distinct classes, i.e., incrusting and non-incrusting.

Of the incrusting salts, carbonate of magnesia is the most objectionable, and any feed water that contains a dozen grains per gallon of magnesia can be expected to have a most injurious effect on the boiler, causing corrosion and pitting. Carbonate of lime, while not as bad as the magnesia carbonate, yet has a very destructive action on a boiler and 20 grains per gallon of this is considered bad water. All silicates, oxides of iron, and aluminium, and sulphate of lime are also incrusting. The non-incrusting substances are three, viz., chloride of sodium (common salt), and sulphate and carbonate of soda.

Note.

In view of the increasing importance laid upon a knowledge of the chemical formation of feed water, these chapters of Chemical Terms and Analysis of Feed Waters are given to indicate the direction in which the advanced engineer must push his inquiries. There are more millions of treasure to be made by properly “treating” the water which enters the steam generators of the world than can be extracted from its gold mines.

An important “point” is to make sure, before adopting any permanent system for purifying the waters of a steam plant, that it is always the same in its ingredients, i.e., that the impurities contained in the water are the same at all times.

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ANALYSIS OF FEED WATER.

In response to a generous offer made by a leading engineering journal, the following compositions of feed water were ascertained and published. The “Directions” show how the water was forwarded, and the tables, the result of careful examination, of samples sent from widely separated sections of the country.

Directions.

1. Get a clean gallon jug or bottle and a new cork (or, at all events, a thoroughly clean one).

2. Wash out the vessel two or three times with the same water that is going to be sent in it. This is to make sure that the sample may not be contaminated with any “foreign” ingredient.

3. Tie the cork, after the bottle is filled with the water, with a strong string or wire. Pack the bottle so secure, with hay or straw, sawdust, or newspapers, that it may not knock itself to pieces against the sides of the box.

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CORROSION AND INCRUSTATION OF STEAM BOILERS.

No more perplexing question presents itself to the engineer and steam user than the one to be inferred from the above heading. Enormous losses of money, danger to life and property and the loss of position and the reputation of the engineer are involved in it. How to avoid these actual evils is of the first importance in steam economy. The subject at first sight seems to the average student a difficult one to master, but like all other matters pertaining to mechanics, investigation that is backed with reason, will show that much that appears obscure is really very plain indeed; this is because nature, even down to the sediment remaining in a boiler after the conversion of water into steam, operates in its formation with infinite exactness and along well known lines.

Boilers corrode on the outside as well as within, and to a great extent unless carefully cleaned and painted; but it is the damage caused by “hard” and acidulated water within the boiler that is to be principally guarded against.

An extreme example of incrustation has been described in that of a locomotive type of a stationary boiler. Its dimensions were: seventy-two inches in diameter, twenty-two feet long, with 153 three-inch tubes; shell, three-eighths; head, three-eighths, and made of iron. The scale against the back head was nearly two inches thick and completely filled the space between the tubes, so that circulation was impossible, the only wonder being that the boiler did not give out sooner than it finally did. The scale was even with the top row of tubes, the143 only part of the boiler generating steam being the fire box and the upper row of tubes, the others acting simply as smoke conduits. There was certainly a great loss of fuel, quite fifty per cent. Had it been a horizontal boiler it would have burned out before the scale became so heavy.

In the above instance, the loss in fuel is estimated at one-half. Careful experiment has proved an average loss of fuel as follows:

¹⁄₁₆ inch of scale causes a loss of 13 per cent. of fuel.
¹⁄₄ inch of scale causes a loss of 38 per cent. of fuel.
¹⁄₂ inch of scale causes a loss of 60 per cent. of fuel.

It must be remembered that dry steam, as it is used through the engine or for other purposes, carries away none of the impurities which pass with the water into the boiler; hence, in a battery of boilers burning, say, 20 tons of coal per day and evaporating 10 lbs. of water to a pound of coal, there is a body of water going through them every day of 200 tons. Multiply this by 300 days for a year = 60,000 tons, and it will be seen how very great is the problem of keeping the interior of the boilers free from scale and deposit.

Chemically pure water is that which has no impurities, and may be described as colorless, tasteless, without smell, transparent, and in a very slight degree compressible, and, were a quantity evaporated from a perfectly clean vessel, there would be no solid matter remaining.

But, strangely, investigation has proved that water of this purity rapidly corrodes iron, and attacks even pure iron and steel more readily than “hard” water does, and sometimes gives a great deal of trouble where the metal is not homogeneous. Marine boilers would be rapidly ruined by pure distilled water if not previously “scaled” about ¹⁄₃₂ of an inch.

Water is formed by the union of two gases—oxygen and hydrogen. These two are simple bodies, formed by the Creator in the beginning, which are found in combination in thousands of different forms. Both when alone are invisible. Take one volume of oxygen and mix it with two volumes of hydrogen and they will chemically unite and form water. This is by144 measure. By weight water is composed of 88.9 of oxygen to 11.1 of hydrogen = 100 parts. See pages 229, 230 for further information.

It is an important point to remember that when water is expanded about 1,700 times into steam, it is simply expanded water, as ice is hardened water, i.e., in expanding into steam the two constituent gases do not separate. Hence, in dealing with the impurities inside the boiler, it is to be observed that in no sense do they change the essential nature of water itself. The impurities are simply foreign bodies, which have no legitimate place in the boiler, and are to be expelled as dangerous foes. As a general principle, it may be stated that it is more profitable to soften and filter the water used in boilers than to trust to blowing out or dissolving the sediment and scale that will be otherwise formed, for observations show that “anti-incrustators” containing organic matter help rather than hinder incrustations, and are therefore to be avoided. For the remedy of foul water there are numerous contrivances to prevent it from entering the boiler, which is far better than trying to extract the sediment after it is there, though there are many ingenious methods for doing that also, some of which will be detailed hereafter.

PRELIMINARY PRECIPITATION OF WATER.

A good method of avoiding incrustations in steam boilers is evidently a preliminary purification of the feed-water, provided it can be done by means sufficiently simple. This is a problem which it is claimed has been solved by M. Dehne of Halle, by means of an arrangement which we will herewith describe. The fresh water, which is taken up by a feed pump, is sent into a heater where it is raised to a temperature that will be favorable to chemical reaction. It then passes into a mixer where it encounters certain reacting agents which have been pumped in there by a pump of special design. These reacting agents are composed of a mixture of carbonate of soda and of caustic soda, the carbonate of soda serving to precipitate the sulphate of lime contained in the feed water, while the caustic145 soda precipitates the carbonate of lime and the magnesia. The relative dimensions between the special pump and the feed pump are calculated in such a way that the proportions of carbonate of soda and caustic soda in the mixture have always a certain relation to the amount of lime and magnesia to be precipitated. The water of the mixture is frequently very much disturbed by the precipitations which are formed, and passes into a filter where all the matters that are held in suspension are retained. It then goes into the boiler. In cases where the feed-water is taken from a tank, the heater, the mixer, and filter are put in the suction pipe of the feed pump, but if, as often happens, the water is already under pressure and will pass directly through the three, the feed pump will take the water directly from the filter and pump it directly into the boiler.

A PRECIPITATOR FOR SEA WATER.

It is quite possible to prepare sea water in such a way as to practically prevent any serious deposit forming from it.

The process employed is to add to the sea water a known quantity of precipitator powder consisting chiefly of soda ash, and having done this in a closed vessel, to heat the mixture by blowing into it waste steam, until a pressure of from 5lbs. to 10lbs. is created; under these circumstances practically all the magnesium and calcium salts separate from the water and are easily got rid of by filtering it under pressure into the hot-well.

A precipitator 6 ft. 4 in. high and 3 ft. in diameter, holds a ton of water, and the time taken, from the first running the sea water in, to its delivery into the hot-well, need not exceed 1 hour and 15 minutes, so that in practice, giving plenty of time between the makes, it would be perfectly easy to prepare 8 to 12 tons in the 24 hours with a small precipitator of the size named. The prepared water has a density of ^l⁄₃₂nd, and may with safety be evaporated until its density is ⁵⁄₃₂nds, the salts present not crystalizing out until a density of from ⁶⁄₃₂nds to ⁷⁄₃₂nds is reached.

In preparing sea water in the way proposed, every precaution must be taken to add slightly less of the precipitant than is necessary to entirely throw down the calcium and magnesium146 salts, as it is manifestly impossible in practice to guard against small quantities of sea water finding way into the boiler either from leaky condensers or else being fed in by the engineer during some emergency, and if under these conditions any excess of the precipitant were present in the boiler, a bulky precipitate would be thrown down and cause trouble, although it would not bind into a solid scale.

Briefly recapitulated the means which are best adapted for preventing the formation of the dangerous organic and oily deposits considered are:

I. Filtration of condensed water through a coke column.

II. Free use of the scum cocks.

III. The use of water of considerable density rather than of fresh water.

IV. The use of pure mineral oil lubricants in the smallest possible quantity.

SCALE DEPOSITED IN MARINE BOILERS.

The analysis given below may be looked upon as typical of the incrustation formed by fresh water, brackish water and sea water respectively in marine boilers:

From this it is evident we may look upon the incrustation from fresh water as consisting of impure calcic carbonate, whilst that from sea water is impure calcic sulphate, the brackish water from the mouths of rivers yielding, as might be expected, an incrustation in which both these compounds are present in nearly equal quantities.

The importance of these differences in the deposit formed is very great, as it enables the shipowner to arrive at the conclusion as to the treatment that the boilers have received during the voyage, by examination and analysis of the scale that those147 boilers contain. Taking, for instance, the case of a ship which uses fresh water both for filling and make up, it is manifest that on her return to port the scale should be very slight and should consist mainly of calcic carbonate, whilst if the scale exceeds ¹⁄₁₆ in., and shows a preponderance of calcic sulphate, it is manifest that such scale could only have been formed by sea water, either leaking in from faulty condensers or being deliberately fed into the boilers.

With the introduction of high pressure steam a new and dangerous form of deposit has added to the trouble of the marine engineer; having entered the boiler, the minute globules of oil, if in great quantity, coalesce to form an oily scum on the surface of the water, or if present in smaller quantities, remain as separate drops; but show no tendency to sink, as they are lighter than water.

Slowly, however, they come in contact with small particles of other solids separating from the water and sticking to them, they gradually coat the particles with a covering of oil, which in time enables the particles to cling together or to the surfaces which they come in contact with. These solid particles of calcic carbonate, calcic sulphate, etc., are heavier than the water, and, as the oil becomes more and more loaded with them, a point is reached at which they have the same specific gravity as the water, and then the particles rise and fall with the convection currents which are going on in the water, and stick to any surface with which they come in contact, in this way depositing themselves, not as in common boiler incrustation, where they are chiefly on the upper surfaces, but quite as much on the under sides of the tubes as on top.

The deposit so formed is a wonderful non-conductor of heat, and also from its oily surface tends to prevent intimate contact between itself and the water. On the crown of the furnaces this soon leads to overheating of the plates, and the deposit begins to decompose by heat, the lower layer in contact with the hot plates giving off various gases which blow the greasy layer, ordinarily only ¹⁄₆₄ inch in thickness, up to a spongy leathery mass often ¹⁄₃ inch thick, which, because of its porosity148 is an even better non-conductor of heat than before, and the plate becomes heated to redness.

When water attains a temperature, as it does under increasing pressure, ranging from 175° to about 420° Fahr., all carbonates, sulphates and chlorides are deposited in the following order:
First. Carbonate of lime at 176° and 248° Fahr.
Second. Sulphate of lime at 248° and 420°.
Third. Magnesia, or chlorides of magnesium, at 324° and 364°.

It is to take advantage of this fact that mechanically arranged jets, sprinklers and long perforated pipes are introduced into the interior of the boiler; these tend to scatter the depositing impurities and also to bring the feed water more quickly to the highest heat possible.

With regard to the oxide of iron or iron salts in solution, these can best be treated with small quantities of lime. By adding re-agents, they set up chemical changes, which result in precipitation, which give the water a milky appearance; they divide into particles, and ultimately settle, leaving the water pure and bright. The mechanical treatment on a limited scale would be easy, a settling tank sufficing; but this becomes a different matter when large quantities have to be dealt with.

ANALYSIS OF AVERAGE BOILER SCALE.

The percentage only of each ingredient the scale is composed of is given, as it cannot be told how much water was evaporated to leave this amount of solid matter.

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A LOCOMOTIVE-BOILER COMPOUND.

The lines of a certain great R. R. traverse a country where the water is very hard and they are compelled to resort to some method of precipitating the lime that is held in solution. After many tests and experiments they have made a compound and use it as follows: in a barrel of water of a capacity of fifty gallons they put 21 lbs. of carbonate of soda, or best white soda ash of commerce, and 35 lbs. of white caustic soda. The cost, per gallon, is about 2¹⁄₂ cents.

The compound is carried in this concentrated form, in calomine cans on the tender of each locomotive. A certain amount, according to the necessities of the case, is poured into the tender at the water tank at each filling. This amount is determined by analysis, and varies all the way from two to fifteen pints to two thousand gallons of water. The precipitating power of this compound may be taken roughly at ²⁄₃ of a pound of the carbonate of lime, or equivalent amount of other material, per pint of the compound. On their western lines where they are dealing with alkali waters and those containing sulphates, the company use merely 60 pounds of soda ash to a barrel of water. When the water is pumped into the boiler the heat completes the precipitation and aggregation of the particles, and this does away with all trouble of the tenders or injector tubes clogging up.

The case is an interesting one to stationary engineers, because where the water is pumped into the boiler from tanks the same compound can be used, provided the water contains the proper constituents to be precipitated by it; and where the water is taken from city water mains, it would be a simple matter to devise an apparatus to admit the compound to the feed pipes.

“Points” Relating to the Scaling of Steam Boilers.

The peculiarity about the sulphate of lime is that the colder the water the more of it will be held in solution. Water of ordinary temperature may hold as high as 7 per cent. of lime sulphate in solution, but when the temperature of the water is raised to the boiling point a portion of it is precipitated, leaving about .5 of one per cent. still in solution. Then as the150 temperature of the water is raised, still more of the substance is precipitated and this continues until a gauge pressure of 41 pounds has been reached which gives a temperature of about 200 degrees; at this point all the sulphate of lime has been precipitated. Many other scale forming substances act in a similar manner. This shows quite plainly that any temperature that can be produced by the use of exhaust steam would not be sufficient to cause the precipitation of all the substances which might be contained in the water.

That boiler incrustations are the immediate causes of the majority of steam boiler explosions is no longer a doubtable question.

Nearly all foreign matter held in solution in water, on first becoming separated by boiling, rises to the top in the form of what is commonly called scum, in which condition much of it may be removed by the surface blow-off. If not removed, however, the heavier particles will be attracted to each other until they have become sufficiently dense to fall to the bottom, where they will be deposited in the form of scale, covering the whole internal surface of the boiler below the water line, with a more or less perfect non-conductor of heat.

It is recorded that the engineer of the French ocean steamer St. Laurent omitted to remove a bar of zinc when repairing and cleaning out his boilers. On opening the boilers at the end of the voyage to his great surprise he found that the zinc had disappeared, but his boilers were entirely free from scale and the boiler plates not injured in the least.

It has been recently determined by some German experimenters that sugar effects a strong action upon boilers. It has an acid reaction upon the iron which dissolves it with a disengagement of hydrogen. The amount of damage done increases with the amount of sugar in the water. These results are worthy of note in sugar refineries and places where sugar sometimes finds its way into the boilers by means of the water supplied. The experimenters in question also find that zinc is strongly attacked by sugar; copper, tin, lead and aluminium are not attacked.

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Two reasons, relating to incrustations, for not blowing out a boiler while under steam pressure may be given as follows: One is, that the foreign matter floating on top of the water will be deposited on the shell of the boiler as the water gradually subsides, and, second, the heated walls of the furnace will communicate a sufficiently high temperature to the boiler to dry and flake the sediment that would otherwise remain in the boiler in the shape of mud, which could easily be washed out were it not for the baking process.

Bark, such as is used by tanners, has an excellent effect on boiler incrustations. It may be used as follows: Throw into the tank or reservoir from which the boilers are fed a quantity of bark in the piece, in sufficient quantity to turn the water to a light brown color. Repeat this operation every month at least, using only half the quantity after the first month. Add a very small quantity of the muriate of ammonia, about one pound for every 2,000 gallons of water used. This will have the effect of softening as well as disintegrating the carbonate of lime and other impurities deposited by the action of evaporation.

Note.—Care must be exercised in keeping the bark, as it becomes broken up, from the pump valves and blow-off valves. This may be accomplished by throwing it into the reservoir confined in a sack.

Among the best samples of boiler compounds ever sent to the laboratory for analysis was found to be composed of:

This solution was formerly sold at a good round figure, but since its nature became more generally known, it is not found in market, but is largely used, consumers putting it up in lots sufficient to last a year or so at a time.

The above is strongly recommended by those who have used it, one pound of the mixture being added to each barrel of water used but after the scale is once thoroughly removed from the152 boiler, the use of sal soda alone is all that is necessary. By the use of ten pounds per week a boiler 26 feet long and 40 inches in diameter in one of the iron mills of New Albany, Ind., has been kept clean of scale equal to a new boiler.

There are other evils sometimes inherent in hard waters over and above the mere production of a crust. Some waters contain a great deal of soluble magnesia salts, together with common salt. When this is the case there is a great chance of corrosion, for the former is acted on by steam at high pressure in such a way that muriatic acid fumes are produced, which seriously corrodes the boiler, and, what is far worse, passes with the steam into the engine, and produces corrosion in the cylinders and other delicate fittings into contact with which the steam passes. All this can, however, be obviated by the removal of the magnesia from the water.

There has not been, and never can be, made a mechanical device which will precipitate all the ingredients contained in a water taken from a natural source of supply, and if it were possible to do so it would be the most ruinous thing one could do for the boilers, as water is the greatest solvent known to chemistry, and its nature is to hold in solution and be impregnated with the different elements it comes in contact with, to a certain per cent., and if its lime, magnesia, and the mineral salts are taken away, and the pure water is pumped into the boilers, it will take up the iron, causing pitting and grooving of the boilers. It is better to let nature take its course, to a certain extent, and neutralize what little mineral deposit forms in the boilers with as small an amount of vegetable matter as possible.

It is well to note that different waters require different treatment; what will be of benefit in one instance will be of no value whatever in a different water, many of the “compounds” sold to prevent and remove scale will certainly destroy a boiler if they are used persistently, because they are composed of the exact opposite chemicals which should be used; as an example it is stated that at one establishment one thousand dollars were expended annually for a mixture which it is said resulted in the reduction of the life and usefulness of the boilers of 50 per cent.

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ENGINEERS’ TESTS

FOR IMPURITIES IN FEED WATER.

Much expense can be saved in fuel and boiler repairs by a little preliminary expenditure of money in securing a supply of good water for the steam boilers of a new establishment. Well water is nearly always inferior to the running water of streams; water from mines is especially hurtful, containing, as they do, large quantities of free sulphuric acid. Wells along the sea shore or on the banks of rivers affected by the tides, are likely to be saturated with chloride of magnesium. It is in determining these points that these ready tests of feed water are most useful.

A thorough and really scientific analysis of feed water is a costly and tedious process, but a simple and perhaps sufficiently accurate test may be made as follows: take a large (or tall) clear glass vessel and fill it with the water to be tested; add a few drops of water of ammonia, until the water is distinctly alkaline; next add a little phosphate of soda; the action of this is to change the lime, magnesia, etc., into phosphates, in which form they are deposited in the bottom of the glass. The amount of the matter thus collected gives a crude idea of the relative quality of sediment and scale-making material in the water.

Water turning blue litmus paper red, before boiling, contains an acid, and if the blue color can be restored by heating, the water contains carbonic acid. Litmus paper is sold by druggists.

If the water has a foul odor, giving a black precipitate with acetate of lead, it is sulphurous.

An experiment may be tried by dissolving common white or other pure soap in a glass of water, and then stirring into the glasses of water to be tested a few teaspoonsful of the solution; the matter which will be deposited will show the comparative amount of the scale-making material contained in the feed water.

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In order to ascertain the proportion of soda to the feed water the following method is recommended:

1. Add ¹⁄₁₆th part of an ounce of the soda to a gallon of the feed water and boil it. 2. When the sediment thrown down by the boiling has settled to the bottom of the kettle, pour the clear water off, and 3, add ¹⁄₂ drachm of soda. Now, if the water remains clear, the soda, which was first put in, has removed the lime, but if it becomes muddy, the second addition of soda is necessary.

In this way a sufficiently accurate estimate of the quantity of soda required to eliminate the impurities of the feed water can be made and the due proportion added to the feed water.

By exercising a little judgment, the use of pure chemicals, with well cleaned vessels, test tubes, etc., the following reagents will determine the character of the most important elements which injure the iron surfaces of a steam boiler.

Carbonic acid is indicated by baryta water.
Sulphates are indicated by chloride of barium.
Chlorides are indicated by nitrate of silver.
Lime salts are indicated by oxalate of ammonia.
Organic matter is indicated by chloride of mercury.

The “base” of the better class of the various patented boiler compounds is tannin (whence tannic acid) and some form of alkali, and if the compounds were to be deprived of these two elements they would be absolutely worthless.

Where they contain, as some certainly do, sal-ammoniac, muriatic, hydrochloric and sulphuric acids, they cannot but act as boiler destroying agents.

Tannin or tannic acid is the principal ingredient used in preparing leather. It is found in a great variety of plants—sassafras root has it in large proportion, the gall nut and the bark of various trees, especially the oak produce it.

It is the presence of this acid that gives their only value to very many “compounds,” tan bark, gum catechu (which sometimes contains one-half part of tannic acid), etc. The155 acid seems to have but little effect where large quantities of sulphate of lime are present, but in waters where carbonate of lime predominates its detersive qualities are more marked.

The records of the Patent Office show that one boiler compound contains 23 per cent. of catechu, and others, 60, 81, 5, respectively, by which may be inferred the large quantity of this agent, which has been sold in combination with other chemicals, principally soda.

Note.

While the product of water steeped in clean tan bark may be favorable in its action upon boiler incrustation, it has been found to be very unsafe, in practice, to use the “tan liquor” taken from the vats. The danger arises from the fact that sometimes during the process of tanning leather, the required acidity cannot be produced by natural fermentation when sulphuric acid is added, in order to bring the liquor to its required strength—in due course, this corrosive substance acts injuriously on the boiler.

USE OF PETROLEUM OIL IN BOILERS.

The use of crude (unrefined) mineral oil in steam boilers is attended by risks caused by impurities and foreign substances mixed with it. These are likely to combine with the earthy matter in the water and tend to form instead of preventing scale; the tar and wax contained in crude petroleum combine with the sediment in steam boilers, and the paste prevents the water from reaching and protecting the plates. This is true particularly in shell boilers which have flat surfaces over the fire. Refined mineral oil has none of these disadvantages.

Kerosene oil has all the advantages to be derived from the use of crude petroleum and the above objections quite removed.

In one system of the application of steam the use of kerosene and petroleum cannot be recommended: that is when live steam is used for cooking purposes, the odor from the oil will impregnate the meat and other products designed for food consumption.

156

KEROSENE OIL IN BOILERS.

Under certain conditions, and with care and judgment, the use of refined petroleum has been found to be of great advantage in removing and preventing scaling in steam boilers.

There is no well authenticated case where a systematic, regular and uniform feed of pure kerosene oil to a steam boiler has failed to operate beneficially upon the scale formation.

The best results are obtained by the use of the oil under the same arrangement that cylinder oil is fed to an engine. The kerosene is sometimes introduced through a one-fourth inch branch to the suction pipe of the feed pump, leading to the vessel containing the oil, so that any quantity, large or small, can be put into the boiler simultaneously with the usual feed. The drawback to this arrangement is that when the feed water heater has to be cleaned, a gallon or more of the oil is often lost, which together with a very unpleasant odor, when used in this manner, tends to condemn its use. But when piped between the boiler and heater, these objections cease. We present an arrangement which is illustrated by cut on page 157.

This is nothing more than a storage system with sight feed, by use of which the oil can be fed drop by drop as desired—for each drop of water entering the reservoir a drop of oil is forced down the small ¹⁄₄-in. pipe, up the glass tube and on into the boiler.

In piping it is necessary to have the water or larger pipe (¹⁄₂ in.) attached through the lower plug as shown in cut, and the oil as shown, going through the smaller or ¹⁄₄-in. pipe—i.e., the oil pipe must, under all circumstances, be the smaller of the two.

In the figure is shown a piece of 6-in. gaspipe, about a foot in length, plugged at each end; the top plug has one opening, for an inch nipple “a” with top. This opening is to be used in filling the reservoir with oil. The bottom plug has two holes, one for the ¹⁄₂-inch water pipe, and the second for a small pet cock “B,” to let the water out, whenever it is necessary to refill the tank with kerosene. The water gauge connection is157 the ordinary, cheap brass fixture, with boxes, nipples, etc., used in boilers, with gasket of rubber bottom and top of the glass. The glass plainly exhibits the depth of water and oil in the reservoir as well as the feed of minute drops of oil as they speed on their beneficent mission softening the injurious scale. There are the usual 2 valves on the water glass; by opening the lower one more or less, the amount of oil used can be regulated to a nicety. The valves can be used to entirely cut off the apparatus at any time desired.

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METHOD OF FEEDING KEROSENE OIL TO BOILER.—Fig. 69.

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Note.—Should the end of the screw connection inside the holder which each one of these valves control, not be ¹⁄₄ inch, a reduced elbow should be used, as ¹⁄₄-in. pipe will give the best satisfaction when used as a stand pipe inside the reservoir.

The quantity of oil to be fed to a boiler is very largely to be determined by experiment commencing with a minimum and increasing the amount as found necessary to keep down the scale formation. The use of 2 qts. of the oil per week has been found to be sufficient for a boiler 4 feet in diameter and 12 feet long, and three quarts per week on boilers 5 feet in diameter. This quantity may be regarded as the smallest advisable to use and from that up to 1 to 2 gallons per diem in boilers, say of 125 horse power, when pushed to their capacity in evaporating water.

The result of careful experiments justifies the use of kerosene, the scale being less than in four years’ previous experience, and a large portion of the boiler showing the clean black steel, in as apparently good condition as when new.

Despite the small quantity of kerosene used in the boilers in this case, the odor was perceptible by opening an air valve to any steam radiator in any of the buildings. When as much as a gallon per week was used, the odor was very strong, but with one half that amount it was hardly perceptible, and only to be noticed when an air valve had been open a long time. And since commencing to use the oil a much greater deposit of rust scales than usual has been found in the various steam traps in the buildings, indicating that the oil is also exerting a cleansing influence on the pipes of the whole system.

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Note.—Provision must be made for the removal of the scale as it drops from the internal surfaces of the boiler, as at times many bushels of it have been deposited directly over the furnace; hence, if a boiler is known to be badly incrusted, the kerosene should not be put in the first time more than three days before it is intended to wash the boiler.

Note 2.—The safety valve should be opened to allow the escape of the gas arising from the kerosene before cleaning out the boiler; where a lighted lamp or candle is used, as it must necessarily be—indeed this is a precaution which ought always to be observed in all cases, viz., properly to ventilate boilers, heaters, and tanks of all descriptions before entering them with lighted lamps and torches. While these gases are not likely to cause an explosion, they burn quite rapidly and should be promptly removed without giving opportunity for an accident.

The accumulation of gas is not confined to the use of kerosene oil for the prevention of scale in steam boilers, but is also found in flour mills, confectioners’, conduits for electric wires, brewers’ vats, etc. So, with common sense precautions, no extra risk is run in using kerosene oil in steam boilers.

MECHANICAL BOILER CLEANERS.

Owing to the fact (1) that nearly, if not quite all, the impurities which exist in feed water are set free by a high temperature attained under pressure; (2) that these impurities are left in the boiler by the constant use of the steam, there follows the result that the water remaining is more and more impregnated with the residuum composed of the foreign matters which (the water removed) constitutes mud, scale, etc.

The custom has been and is now to regularly “blow off” one or two gauges of this water once or twice per day replacing it with fresh water of less density; that this is a very imperfect method for removing the foreign matter is readily allowed, besides wasting absolutely all the units of heat contained in the water blown off.

Now, within the boiler while in use, under the operation of the fierce heat of the furnaces, are constant changes in the160 position of the water caused by the boiling, by the withdrawal of the steam and by the constant effort of the hot water to rise and the cold water to fall. The water thus keeps in circulation everything within the boiler, including the sediment, except in places where the water is from any cause without motion. In these quiet nooks there is a constant depositing of the elsewhere active foreign matters contained in the water, which deposits, in the form of mud and scale, left undisturbed, causes loss and danger.

It is in taking advantage of these facts, and of the principles of the circulation of hot and cold water, that mechanical boiler cleaners are brought into successful use.

These devices for the stilling of the water and collection of the sediment are made in various forms and all sizes and capacities, and are located at the sides or back of the boiler setting and even on top of the boiler. There is a system where pipes in a coil are fixed in the sides of the furnace and exposed to its greatest heat, and which, owing to their enlarged area, act as most efficient reservoirs. In all these devices there is an upflow pipe connected with the lower and coolest water, and a return pipe connecting with the top of the water where it is hottest. This arrangement assures a constant current which is more or less rapid according to the intensity of the fire and which keeps up as long as the firing is done. Where this current passes through the reservoir, the enlarged area and comparative quiet is favorable for the deposit of the sediment and in practical experience it does deposit nearly all of it. The collection of the impurities is helped by a funnel-shaped appliance placed at the opening of the upflow pipe, which, aided by the rapid flow of the hot water, carries the floating scum towards it into the reservoir. Attached to the reservoir is the blow-off pipe through which the deposited matter is removed as often as necessary.

The use of these mechanical cleaners is readily understood: (1) they provide a place of accumulation for the sediment; (2) they save the necessity of opening the boilers to remove by hand, the refuse of the boiler; (3) save fuel by avoiding the necessity of frequent blowing off one or two gauges of water, and (4) by the preventing the formation of scale with its attendant evils.

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SCUMMING APPARATUS.

In addition to the bottom blow-out apparatus every boiler should be provided with means for blowing out water from the surface in order to remove the fine particles of foreign matter floating there, which afterward settle and consolidate as scale on the heating surfaces.

Fig. 70.
Scum Cock

It consists, in its simplest form, of a pan, or a conical scoop, near the surface of the water, but below it, connected with a pipe passing through the boiler-shell, on which is a cock, or valve, for regulating the escape of the water laden with the impurities deposited in the pan. There are patented apparatus for this purpose which are well designed and easily fitted to a boiler.

The office of the surface blow-off, illustrated in Fig. 70, is to remove the foreign matter which is precipitated from its solution in the water.

A surface blow-off used occasionally will remove the greater portion of this scum and keep the boilers reasonably free from scale and mud. Where dirty or muddy water is fed into the boilers the surface blow-off is one of the cheapest and most efficient means for keeping the boiler clean. The efficiency of the surface blow-off is not so great as that of some of the mechanical boiler-cleaners, as by their use it is not required that any hot water shall be wasted, and this is the greatest objection to the surface blow-off, as in the hands of some people a large amount of boiling water is wasted each time it is used. But both of these arrangements are virtually skimmers, as they remove the precipitated mineral and vegetable matter from the surface of the water in the boiler. One does it by blowing out162 the scum and some water at the same time, while the mechanical boiler-cleaner removes the scum, but returns the water to the boiler.

There are several efficient ways of arranging a surface blow-off. The principal part of the blow-off is a pan or perforated pipe placed horizontally at the water level having a pipe leading outside the boiler to any convenient place where the scum may be blown. When a perforated pipe is used the action is to force the scum from the top of the water during the time the valve is open, and blow it through the pipe. In using an apparatus of this kind it should be blown often, but only for a moment at a time, as all the scum near the pipe is removed immediately, and to keep the valve open longer than necessary to remove the scum near the pipe would allow the escape of clean water or steam which would be wasteful. If a pan is used and is fastened so that the top is secured at the ordinary water level, as shown in Fig. 70, the blow-off pipe leading from near the bottom of the pan, it will be more efficient than the perforated pipe arrangement as it will not require to be used so often, and the waste of water and steam will not be so great. The pan, by producing an eddy in the water, causes all the scum to gather over the top, and as the water is quiet there it will gradually settle into the pan, where it will remain as mud. When the blow-off valve is opened the greater part of the mud which is gathered is blown out, and but very little water is carried with it.

USE OF ZINC IN MARINE BOILERS.

Zinc has been used in marine boilers for many years, but it was not until the publication in 1880 of the report of the Admiralty committee that the use of zinc became general. It has been used in various ways: 1.—Virgin spelter, as imported in oblong slabs of various sizes. 2.—Cast, or remelted zinc. 3.—Cast zinc buttons, generally made from virgin spelter or new clean zinc trimmings. 4.—Zinc spheres. 5.—Rolled zinc blocks, generally 12 inches by 6 inches, and thicknesses varying from ¹⁄₄ inch to 1¹⁄₂ inch, generally with a ¹³⁄₁₆-inch hole in the centre.

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It is desirable that close-grained zinc of uniform structure and free from impurities should be used, and rolled zinc appears to meet this want. The wear is entirely confined to the surface. It does not appear to become distorted or broken up. On the contrary, it gradually wastes away till only a slight shred, a sort of skeleton frame work, remains to indicate what it has been.

The primary object in the use of zinc in boilers is the prevention of corrosion, but it has also some effect in reducing the amount of incrustation, and rendering it softer and less adherent.

Table

Showing Amount of Sediment collecting in a steam boiler when evaporating 6,000 gallons per week, of 58,318 grains each.