PART VIII.
THE BOILER ATTACHMENTS.
QUESTION 123. _How is water supplied to the boiler to replace that which is converted into steam?_
_Answer._ It is usually forced into the boiler against the steam pressure by force pumps, but another instrument called an _injector_ is now much used.
QUESTION 124. _What is the form of construction and principle of the operation of such force pumps?_
_Answer._ The ordinary single-acting force pump, fig. 66, used on locomotive and other steam engines consists of a _pump-barrel_, _A A_, which is a cast-iron or brass cylinder in which a tight-fitting piston, _B B_, called the _pump-plunger_, works. This piston or plunger is simply a round rod which works air-tight through what is called a _stuffing box_, _C_, whose construction will be fully explained hereafter. The plunger receives a reciprocating motion, usually from the piston-rod of the engine, but is sometimes worked by a small crank attached to one of the crank-pins, or by an eccentric on one of the axles. The pump-barrel is connected with the water-tank of the tender by the _suction-pipe_, _D_, and with the water-space of the boiler by the feed-pipe, _E E_. Over the suction-pipe _D_ is a valve, _F_, called the _suction-valve_, which opens upward, and below the feed-pipe, _E_, is another valve, _G_, called the _pressure-valve_. These valves are cylindrical and made of brass, and rest on brass seats, _g_, _g_, to which they are fitted so as to be water-tight. They work in guides, _k_, _k_, called _cages_, the form of which is more clearly shown in the section, fig. 67, and the plan, fig. 68. When the plunger is drawn out of the pump-cylinder it creates a vacuum behind it, and the pressure above the valve _G_ closes it, while the atmospheric pressure on the water in the tank forces it into the suction-pipe, opens the valve _F_, and fills the pump-cylinder. When the plunger is forced back again the force with which it presses against the water in the pump-barrel, _A_, closes the valve _F_, and opens the pressure-valve _G_, and the water is then forced through the feed-pipe into the boiler. In order to be certain that the water in the boiler will not flow back into the pump, and also to prevent all the water and steam in the boiler from escaping in case of accident to either the feed-pipe or pump, another valve, _H_, fig. 66, called a _check-valve_, is placed between the feed-pipe and the boiler. The construction of this valve is similar to that of the pressure and suction valves. It is inclosed in a cast-iron or brass case, _I I_. All of these valves have cages in which they work and which also act as stops, which prevent them from rising from their seats further than a certain distance. This distance is called their _lift_, and the successful working of the pumps depends very much on the amount of lift which the valves have. This is usually from ³⁄₁₆ to ¹⁄₂ inch.
[Illustration: _Fig. 66._]
[Illustration: _Fig. 67._]
[Illustration: _Fig. 68._]
Over the pressure-valve _G_ is a chamber, _J_, called an air chamber. When water is forced into this chamber, it is obvious that as soon as it rises above the mouth of the pipe _E_, the air above the surface, _c d_, of the water will be confined in this chamber. This confined air, being elastic, will be compressed and expanded by the pressure of the water, so that it forms a sort of cushion, which relieves the pump and the pipes from the sudden shocks to which they are subject, owing to the rapid motion of the pump-plunger.
Another air-chamber, _K K_, is sometimes placed below the suction-valve _F_. The object of this is to supply a cushion to relieve the suction-pipe from the shock which is caused by the sudden arrest of the motion of the water in the pipe when the valve _F_ is closed. When the pump-plunger is drawn out, the water flows through the valve _F_ to fill the vacuum in the pump-barrel, _A A_, and consequently all the water in the suction-pipe is put in motion. As soon as the plunger returns, the valve _F_ is closed and the motion of the water is suddenly arrested, thus producing more or less of a shock in the pipe _D_. When the water in the air chamber _K K_ rises above the line _a b_, it is evident that the air above that line will be confined in the space surrounding the pipe _L_. This air then forms a cushion in the same way as that in the upper air chamber _J_ does, which has already been explained. The advantages of the lower air chamber are, it is thought, more imaginary than real.
QUESTION 125. _How can the pump be taken apart and the valves examined?_
_Answer._ By removing the bolts _e_, _e_, the upper air chamber can be taken off, and by taking out the bolts _f_, _f_, the lower one can be taken down, and the valves and cages removed. The check-valve _H_ can be taken out by removing the bolts _l_, _l_, which hold up the valve-seat _h_ and the valve and cage.
QUESTION 126. _How can it be known whether the pump is forcing water into the boiler?_
_Answer._ To show this a cock, called a _pet-cock_, is attached to the upper air chamber in the position shown by the dotted circle _m_.[33] By opening this cock, if the pump is working, a strong jet of water will be discharged from it during the backward stroke of the pump-plunger. If the pump is not forcing water into the boiler, or is working imperfectly, the stream discharged from the pet-cock will be weak, and the backward and forward strokes of the plunger will thus not be very definitely indicated by the discharge from the pet-cock.
[33] The pet-cock is sometimes attached to the feed-pipe.
Another small cock is often attached to the lower air chamber, or to the feed-pipe, to allow the water to escape from the pump in cold weather, when the engine is not working, so as to prevent it from freezing.
QUESTION 127. _Why is it necessary to be able to regulate the quantity of water which is forced into the boiler by the pumps?_
_Answer._ Because when the engine is working hard, that is, pulling a heavy load up a grade, more steam and consequently more water are consumed than when it is not working so hard, and therefore more water must be forced in to supply the place of that which is used in the form of steam. If more water is forced in than is consumed, the water will rise and fill the steam-space and a part of it will then be carried into the cylinders without being evaporated. If too little water is forced into the boiler, the heating surface will not be covered, and there will consequently be danger that those portions which are exposed to the fire will be overheated and injured.
QUESTION 128. _How is the supply of water which is fed into the boiler by the pump regulated?_
_Answer._ By a cock in the suction-pipe called a _feed-cock_, which can be regulated by the locomotive runner, so that more or less water is supplied to the pump. There is also a valve in the water tank by which the supply of water can be regulated.
QUESTION 129. _On what part of the locomotive are the pumps usually placed?_
_Answer._ They are usually attached to the frames behind the cylinders, and are worked by the piston-rod, as will be more fully explained hereafter; but they are sometimes placed inside of the frames, that is, between the wheels, and worked from an eccentric on one of the axles, and sometimes they are placed outside of the wheels near the back part of the locomotive, and worked from short cranks attached to the crank-pins.
QUESTION 130. _What provision is made for preventing the water in the pumps from freezing in cold weather?_
_Answer._ Pipes which communicate with the steam-space of the boiler are attached to each of the suction-pipes, so that, by opening valves in the former, steam is admitted into the suction-pipes to heat the water in them. By admitting this hot water into the pump, it is kept warm, and the water is thus prevented from freezing.
[Illustration: Fig. 69.]
QUESTION 131. _What is an “injector”?_
_Answer._ It is an instrument in which a jet of steam from the boiler mingles with and forces a continuous jet of water into the same boiler against its own pressure.
QUESTION 132. _What is the action of the injector and what are the names of its essential parts?_
_Answer._ All injectors have certain parts in common. These may be shown in the simplest form of instrument, as in the fixed-nozzle injector, a section of which (omitting all detail of construction) is shown in fig. 69.
The steam from the boiler, passing through the pipe _A_, enters the _receiving-tube C_. Here it is joined by the water which enters the pipe _B_. The water condenses the steam in the _combining-tube D_, and a water jet is formed which is driven across the _overflow_ space _F F_, and enters the _delivery-tube H_, thence past the _check-valve I_ into the boiler. During the passage of the water from _D_ to _H_, as it passes across the _overflow_ space _F_, if too much water has been supplied to the steam, some will escape at this point and flow out through the _overflow nozzle G_, while if too little water has been supplied, air will be drawn in at _G_, and carried into the boiler with the water. The names of the essential parts seem very applicable when we notice that steam is _received_ from the boiler at _C_, _combines_ with the water at _D_, and both are _delivered_ to boiler through _H_.
QUESTION 133. _How is the operation of the injector explained?_
_Answer._ Steam escaping from under pressure has a much higher velocity than water would have under the same pressure and condition. The escaping steam from the _receiving-tube_ unites with the feed-water in the combining-tube, and gives to this water a velocity greater than it would have if escaping directly from the water-space in the boiler. The power of this water to enter the boiler comes from _its weight_ moving at the _velocity_ acquired from the steam, and it is thus enabled to overcome the boiler pressure.
This can be illustrated with a wooden croquet ball, which will float on the surface of water and will require considerable force to make it sink. If, however, it is thrown violently into the water, it will sink to a considerable depth before its buoyancy will overcome its momentum, or _actual energy_. If, however, we were to take a very light, hollow wooden or india-rubber ball, no matter how violently we throw it into the water, it will not sink, because the total _actual energy_ of any body IS PROPORTIONAL TO ITS WEIGHT MULTIPLIED BY THE SQUARE OF ITS VELOCITY, and therefore if we throw the hollow ball at the same velocity as the solid one, the former will still have much less energy than the latter. Now, as already stated, steam under a given pressure escapes from an orifice with a very much greater velocity than water. But steam being very light, if its weight is multiplied by its velocity its total energy will be comparatively small. Now in the injector, a portion of the high velocity of steam is imparted to the heavy water, because this water is presented to the action of the steam, not in a mass, as in the boiler, but in small quantity and in such a position that it can easily escape, so that it gradually acquires as high a velocity as the escaping steam can impart, and at the same time the steam is condensed, and therefore there is a heavy substance with a high velocity, whose actual energy is sufficient to overcome the pressure in the boiler. If the steam were not condensed we would have a comparatively light substance moving at a high velocity, which, as has already been explained, would have little actual energy, and would therefore not overcome the boiler pressure.
QUESTION 134. _Does this involve any principle like a perpetual motion, or of work done without consumption of power?_
_Answer_. No, the steam escapes _as steam_, and is returned to the boiler _as water_ with its bulk reduced, say 1,000 times, and if it carries with it twenty times its weight of fresh feed-water, there would still be a loss of pressure or effective force in the boiler sufficient to do the work required in introducing the water.
QUESTION 135. _Will the injector feed hot water?_
_Answer._ The instrument will not work when the feed-water is too hot to condense the steam, for the reasons given above, and the amount of water thrown is always the greatest when the feed-water is the coldest. Steam at a low pressure can be condensed more readily than steam of higher pressure, because it contains less heat. The feed-water may be used hotter to condense low steam than to condense high steam. In using the injector, the lower the boiler pressure the hotter may be the water within certain limits, the limit being the possible condensation of the steam.
QUESTION 136. _Will a “fixed-nozzle” injector, such as has been described, answer as a boiler feeder on locomotives?_
_Answer._ It will answer at some one pressure of steam, to which pressure it may have been adapted in making the instrument, and at that pressure it will work admirably; but it will not work satisfactorily at any other pressure, either higher or lower, and has not much range in quantity of water delivered.
QUESTION 137. _What is required to make an injector work at different pressures?_
_Answer._ The instrument must be so made that the water passage between the receiving tube and the combining tube can be varied in size. This is usually done by making the combining and receiving tubes conical and moving the former to or from the latter, thus contracting or enlarging the water space. Such adjustment must be made at each change of steam pressure in the boiler. If this adjustment is made _by hand_, as in some kinds of injectors, it requires constant attention, if the steam pressure varies frequently.
QUESTION 138. _How has this regulation been accomplished without such attention?_
_Answer._ In the SELF-REGULATING INJECTOR, fig. 70, by using the escape water at overflow to push the combining tube towards the receiving tube and the indraught of water at the same place to pull the combining tube away from the receiving tube. This can be explained as follows:
The case _G_ of the instrument has two inlets, one for steam, the other for water, the two being separated by the plate _F F_. Steam passes into the _receiving tube A_, and its escape is regulated by a taper-plug in the end of the rod _B_, moved by the handle _H_. At the upper end of the _combining tube_ _C_, where it swells out into a bell mouth, is a piston _N N_, sliding in the case. The lower end at _C_ is guided by the upper end of the _delivery tube_ _D_. The delivery tube _D_ is stationary. The _overflow_ opening is at _O_. The action of this instrument may be thus described: Steam entering the receiving tube _A_ escapes through its lower end when the plug _B_ has been drawn back. It unites with the water surrounding it in the space _N N_, is condensed and passes with the feed-water into the delivery tube _D_, and thence into the boiler. If too much water enters the combining tube, some will escape at the overflow _O_, and filling the space below the piston _N N_, will force the combining tube up toward the receiving tube, and, thus contracting the space between them, will diminish the water supply; while, if it gets too little water in this space, it will take some in at the overflow _O_, and thus draw down the piston _N N_, and enlarge the space, giving more water to the instrument. This self-regulating principle enables the instrument to continue working efficiently, no matter how much the steam pressure in the boiler varies.
[Illustration: Fig. 70.]
QUESTION 139. _How do you start this kind of injector?_
_Answer._ The instrument just described is the latest form of self-regulating injector, manufactured by Messrs. Wm. Sellers & Co., and is called by its makers the INJECTOR OF 1876. It is started and stopped by a simple movement of the lever _H_. This lever _H_ moves a cross-head _I_, on the guide-rod _J_; it also, by means of stops _T_ and _Q_, on rod _L_, opens and closes the starting-valve _K_. In fig. 70 the instrument is shown shut off, and with the starting-valve _K_ open. On the rod _B_ are two valves, a small one _W_ and a larger one _X_. A stop or collar is shown a short distance beyond the large valve _X_. If the lever _H_ be drawn back until this collar comes in contact with the valve _K_, it will have raised the valve _W_ from its seat, and steam will escape through a small passage in the centre of the conical regulating plug. The steam so admitted is sufficient to lift the water, which will then be driven through _D_, and past the valve _K_, and escape at _P_. Drawing back the lever _H_ to the end of its stroke, after the water has been lifted, the large valve _X_ is raised, and the lug on the lever _H_, coming in contact with the stop _T_, on the rod _L_, the valve _K_ is closed. The jet is fully established and the water is driven into the boiler. At the entire end of stroke of the lever _H_, the latch _V_ falls into notches on the rod _J_, when, as the lever is moved forward toward the position shown in fig. 70, this latch will click over the notches and hold the lever in any desired position between the maximum and minimum delivery.
QUESTION 140. _What attachments are needed besides the instrument to render it effective?_
_Answer._ A globe-valve should be placed in the steam pipe leading to the injector, to be closed only when there is occasion to remove the injector when steam is up, and in cold weather, to prevent the condensation of steam in the pipes at the end of its trips. During all the working time of the injector, this valve should be wide open.
QUESTION 141. _In what position, and in what location on the engine should the injector be placed?_
_Answer._ On the right hand side, high enough up to have an air chamber below the injector, above the top of the water in the tank when the latter is full.
QUESTION 142. _What is required to keep the instrument in working order?_
_Answer._ Constant use is better than occasional use. Having two injectors on the same engine, one on each side, the one on the runner’s side will be used while running. The one on the other side should be used when standing. All pipe connections must be tight, so as to prevent the leaking of air. The pipe carrying steam to the instrument should be from such part of the boiler as will insure the use of dry steam, and the waste pipe must not be contracted. The instrument represented in the engraving is the injector of 1876, manufactured by Messrs. William Sellers & Co. of Philadelphia. Beside this, Mack’s and several other kinds of injectors are now used.
[Illustration: Fig. 71.
Scale, ³⁄₈ in. = 1 foot.]
LIST OF PARTS DESIGNATED BY LETTERS OF REFERENCE IN FIG. 71.
_A_, Furnace Door. _B_, _B_, Driving Wheels. _C_, Driving Axle. _D_, _D_, Suction Pipes. _E_, Ash Pan Damper. _F_, _F_, Foot Steps for getting on and off the Locomotive. _G_, _G_, Hand Holds for getting on and off the Locomotive. _H_, _I_, Cab. _J_, _J_, Doors in front of Cab. _K_, _K_, Windows in front of Cab. _L_, Steam Gauge. _M_, Spring Balance. _N_, Steam Gauge Lever. _O′ O_, Throttle Lever. _P_, Water Gauge. _Q_, Stand for Tallow Can. _R_, Drip Pipe for Gauge Cock. _T′ T_, Rod for operating Feed Cock. _T′_, Regulator for Feed Cock. _U V_, Reverse Lever. _W_, Whistle. _X_, Blow-Off Cock. _Z_, _Z_, Frames. _a_, _a_, Heater Cocks. _a a′_, Heater Pipe. _b_, Blower Cock. _c_, _c_, Oil Cups for oiling Main Valves. _d_, Handle for opening Valves in Sand Box. _e_, _e_, Handles for opening Pet Cocks. _f_, Handle for opening Cylinder Cocks. _g_, Whistle Lever. _h′_, Whistle Handle. _h_, Rod connecting Whistle Handle to Whistle Lever. _j_, Handle for left hand Feed Cock. _m m_, Lever for shaking Grate Bars. _n_, Bell Crank for opening front Ash Pan Damper. _o_, _o_, Check Chains. _p_, Pipe for carrying off water from Gauge Cocks. _s_, _s_, _s_, _s_, Gauge Cocks. _w_, Handle for opening Blow-Off Cock.
QUESTION 143. _How can the height of the water in the boiler be known?_
_Answer._ Two appliances are used by which the height of the water in the boiler can be observed. These are: 1. _Gauge_ or _try cocks_. 2. The _glass water gauge_.
[Illustration: Fig. 72. Scale ¹⁄₄.]
[Illustration: Fig. 73.
Scale, 3 in. = 1 foot.]
Every locomotive is provided with four or more gauge-cocks, which are usually placed at the back end of the boiler, where they can easily be seen and reached. These cocks, _s_, _s_, _s_, _s_, are shown in fig. 71, which represents the back end of a locomotive, and to which frequent reference will be made. They are also shown on a larger scale in fig. 72, which represents the end plate of the boiler in section. They communicate with the inside of the boiler and are so placed that one is three or four inches above the other. The two upper cocks are placed above the point where the surface of the water should be when the engine is working, and the two lower ones below it, so that the upper ones communicate with the steam space and the lower ones with the water. When these cocks are opened, if the water is at its proper height, steam is discharged from the two upper ones, and water from the two lower ones.
When a gauge-cock which communicates with the steam space is first opened, it is usually filled with condensed water, so that it should usually be kept open for a little while until this water is discharged. If the upper cocks are opened and continue to discharge _water_, they indicate that there is _too much_ water in the boiler; on the other hand, if steam is discharged when the lower cocks are opened, then there is too little water in the boiler, and the heating surface is in danger of being exposed to the fire without being covered with water, and consequently overheated, or as it is called “burned,” and so injured as to become too weak to bear the strain to which it is subjected by the pressure of the steam. There is then great danger that the crown sheet may be crushed down by the pressure of the steam above it, or that the boiler may be exploded. Even if no accident occur, the boiler is in great danger of permanent injury from overheating when the water is allowed to get too low.
Below the gauge-cocks _s_, _s_, _s_, _s_, fig. 71, an inclined cylinder, _R_, called a _drip-pipe_, is placed with openings to receive the water and steam which are discharged from the cocks. This water is conducted away by the pipe _p_.
The _water-gauge_, _P_, fig. 71, which is shown in section in fig. 73, consists of an upright[34] glass tube, _a a_, which is from one-half to three-quarters of an inch in diameter, and from 12 to 15 inches long. The glass is about one-eighth of an inch thick. At its ends it communicates with the steam and water of the boiler through brass elbows, _b_, _c_. The openings in these elbows, which communicate with the boiler, are closed by the valves or plugs, _d_, _e_, which are worked by screws and handles, _f_, _g_. The glass tube, when it is attached to the elbows, is made steam-tight by rubber rings, which are pressed tight around the tube by _packing-nuts_, _h_, _i_. The elbows are provided with the valves, _d_, _e_, so that in case the glass tube breaks the steam and water can be shut off, so as not to escape through the elbows. The lower elbow is provided with a blow-off cock, _k_, through which any sediment or dirt which collects in the glass tube or elbows can be blown out. When the valves in the upper and lower elbows are opened the steam flows into the glass tube through the upper one, and water through the lower one, and the water assumes a position in the glass tube on a level with the surface of that in the inside of the boiler; that is, the position of the water in the boiler becomes visible in the glass tube. On account of the constant variations of the water in the boiler, the column of water in the glass never remains stationary, but plays up and down as long as the boiler is working. But if the communication between the glass tube and the boiler is closed, then the water in the tube becomes stationary and the water gauge is useless. In order that there may be no obstruction of the glass tube by mud or dirt from the water, it must be _blown out_ often. To do this the lower valve, _e_, is closed, and the blow-off cock, _k_, and the steam valve, _d_, are opened. The steam pressure in the tube on top of the column of water will force it out of the blow-off cock, and the mud and dirt will be carried with it.
[34] Sometimes these tubes are, for convenience, inclined, as shown in fig. 71.
If from any cause the glass tube is broken, first of all the water-valve _e_ should be closed and then the steam-valve _d_, so as to prevent the hot water and steam which will escape from the broken glass from scalding those who are working the engine. By unscrewing the nuts _h_ and _i_ the old glass can easily be removed and a new one substituted in its place.[35] Care should be taken in putting in new glasses not to screw the packing nuts down any more than just sufficiently to make the rubber rings steam-tight around the glass tubes. If they are screwed too tight they are apt to produce a strain on the tube, so that the slightest expansion by heat or contraction from cold will break it.
[35] Extra glasses should always be carried with an engine so as to be substituted in case of accident to the one in use.
[Illustration: Fig. 74.
Scale 1¹⁄₂ in. = 1 foot.]
[Illustration: Fig. 75.
Scale 1¹⁄₂ in. = 1 foot.]
QUESTION 144. _How is the steam pressure in boilers prevented from exceeding a certain limit?_
_Answer._ By what are called _safety valves_. These consist of circular openings, _a_, fig. 74, about three inches in diameter placed usually on the top of the dome,[36] and covered by a valve, _b_, which is pressed down either by a lever, _c c′_, and spring, _d_, as shown in fig. 74, or by a spring alone, as in fig. 76. Two of these valves are usually placed on the top of the dome, so that if one gets out of order the other one will allow the steam to escape as soon as its pressure exceeds that which, it has been decided, the boiler can safely bear. This pressure, in locomotive boilers, is usually from 100 to 130 pounds per square inch.
[36] One of these, _v_, is shown in fig. 41.
QUESTION 145. _How is the amount of pressure which must bear on top of a safety-valve determined?_
_Answer._ This pressure is determined BY MULTIPLYING THE AREA OF THE OPENING FOR THE VALVE IN SQUARE INCHES BY THE GREATEST STEAM PRESSURE, IN POUNDS PER SQUARE INCH, WHICH THE BOILER IS INTENDED TO BEAR. Thus, if the opening for a safety-valve is three inches in diameter, its area will be seven square inches, and, therefore, if the greatest steam pressure which it is intended that the boiler shall bear is 100 lbs. per square inch, the valve must be pressed down with a pressure equivalent to 7 × 100 = 700 pounds. If the pressure on the valve is produced by a lever, as in fig. 74,[37] then the total weight of the safety-valve must be MULTIPLIED BY THE SHORT ARM OF THE LEVER, (or the distance _A_ between the centre of the fulcrum _e_ and that of the load _f_,) AND DIVIDED BY _B_, THE TOTAL LENGTH OF THE LEVER. In fig. 74 the short arm of the lever is 3¹⁄₂ inches, and the whole length 35 inches; therefore if the valve is to be pressed down with a pressure of 700 pounds, the pressure on the end of the lever would be calculated as follows:
700 × 3¹⁄₂ ---------- = 70 lbs. 35
[37] The lever is represented in the engraving with a piece broken out, in order to save room.
The spring _d_ must therefore pull down on the end of the lever with a tension equal to 70 pounds. When the pressure of the spring bears directly on the valve, as shown in fig. 76, then the tension of the spring must be just equal to the pressure on the valve. This tension is produced by screwing down the nuts, _c_, _c_. The spring _d_, which produces the requisite pressure on the end of the safety-valve lever, fig. 74, is arranged inside of two cylinders, _g_ and _h_, which slide over or into each other like the sections of a telescope. This arrangement is called a _spring-balance_. The spring, _d_, is attached to the covered ends and draws them towards each other. The upper cylinder _g_ is connected by a rod, _i_, to the flattened end of the lever _c′_, which has a hole drilled through it to receive the rod. The other end of the rod is screwed into the upper cylinder _g_. This rod is sometimes arranged so that it can be either lengthened or shortened by the nut _j_. By lengthening or shortening the distance, the tension of the spring is either diminished or increased. The lower cylinder of the spring-balance, represented in fig. 74, is attached to a lever, _m_, which is fastened to the back of the _steam-gauge k_. This is shown more clearly by fig. 75, which represents the back of the gauge, and also the lever, _l m_, whose fulcrum is at _m_. The spring-balance is attached to the lever at _k_. By drawing down the lever the tension of the spring is increased, and by raising it up it is diminished. The lever is held in any desired position by the latch, _n_, and the ratchet _r r_. By this contrivance, which is employed on the engines built at the Grant and also at the Baldwin Locomotive Works, the pressure on the valve can at once be either increased or diminished, which it is often desirable to do, especially when an engine is not at work. The spring-balance is shown in fig. 71, and is indicated by the letter _M_ and the lever by _N_. Unless the pressure of the steam exceeds that on top of the valve, it will of course not be opened. As there is always danger that a safety-valve or some of its attachments may become corroded or otherwise disordered, so that it will not act promptly or with certainty, it is desirable to open it frequently, so as to be sure that it is in good working order. To do this the pressure on the valve must be reduced below that in the boiler, which can very conveniently be done with the _spring-balance_ lever which has been described.
The lower cylinder of the spring-balance sometimes carries an index or pointer, _t_, fig. 74, which protrudes through a slot in the cylinder _g_, and indicates the amount of pressure of the spring on a scale marked along the slot on the outside of the cylinder. If it is desired that the safety-valve should open when the steam pressure reaches 100 or any other number of pounds per square inch, the spring-balance is subjected to a tension which will bring an amount of pressure on the top of the safety-valve equal in pounds per square inch of its surface to that of the steam pressure desired.[38]
[38] In loading a safety-valve allowance must always be made for the weight of the lever and the valve.
There should always be some provision made which will render it impossible to increase the steam pressure beyond that which it has been determined that the boiler will safely bear. This is usually done by arranging one of the safety-valves with a lever, as shown in fig. 74, and the other without, like that in fig. 76. The latter is often covered and sealed or locked up, so as to be beyond the control of the locomotive runner.
The safety-valves are usually fitted into conical seats, _S S_, figs. 74 and 76, so as to be perfectly steam-tight, and are made with wings or guides, _t_, _t_, the form of which is shown in the sectional plan _A_, figs. 74 and 76, under the valve. These guides are intended to keep the valves in the proper positions in relation to their seats.
[Illustration: Fig. 76. Scale ¹⁄₈.]
As soon as the steam pressure under the valves becomes greater than the pressure of the springs on top of them, the valves will be lifted up and the steam will escape until the pressure in the boiler is relieved. It will be seen, however, that although the surface of the valve which is exposed to the pressure of the steam is equal to the area of the opening for the valve, after it is lifted from its seat and the steam escapes all around the edge, a larger surface will be exposed to the pressure of the escaping steam. For this reason, it will be found that after a valve is opened steam will escape, or “_blow off_,” as it is termed, until the pressure is several pounds lower than it was when the valve first opened. Advantage has been taken of this fact in the valve shown in fig. 76, which is called the “Richardson” valve, which is now much used. The top of this valve is made larger in diameter, so as to expose more area to the escaping steam. Grooves are also made around the edge of the valve and the seat. These, it is claimed, produce some sort of reflex action of the steam, which keeps the valve open longer than it otherwise would be.
[Illustration: Fig. 78.]
[Illustration: Fig. 77.]
QUESTION 146. _How is the steam pressure in the boiler indicated?_
_Answer._ By an instrument called a _steam-gauge_. There are a great variety of such instruments made, but they may all be divided into two classes, and they all operate upon one of two principles. In the one class the pressure of the steam acts upon a diaphragm or plate of some kind, as shown in fig. 77, which represents a section of a gauge of this kind; _a b_ is a metal plate made with circular corrugations, as shown in section and also by the shading in fig. 78, which represents a front view of the gauge with a part of the dial-plate removed. The steam enters by the pipe _c_ and the small opening _d_, and fills the chamber _e_ behind the metal plate or diaphragm. The corrugations of the latter give it sufficient elasticity, so that when the pressure is exerted behind it, it will be pressed outward by the steam. If it were flat, it is plain that it would not yield, or only to a very slight degree, to the pressure of the steam. In the centre of the diaphragm on the outside is a pin or stud, _f_, which bears against the plate. This stud is attached to a bent lever or “_bell-crank_,”[39] _g h k_, whose fulcrum is at _h_. To the outer end, _k_, a rod, _l_, figs. 77 and 78, is attached, the lower end of which is connected to the short arm _m_ of a toothed segment, _n_, whose fulcrum is at _o_. This segment gears into a small pinion, _p_, which is attached to a spindle or shaft, which carries a pointer, fig. 78. It is obvious now that if the diaphragm, _a b_, is pressed outward, it will move the bent lever _k h g_, the motion of which will be communicated by the rod _l_ to the toothed segment _n_, which will in turn revolve the pinion _p_, and thus move the hand or index. We have selected for this illustration one of many forms of this kind of gauge. The mechanical appliances for communicating the motion of the diaphragm to the index or pointer are different in the gauges made by different manufacturers. The form of the diaphragm also differs. In some cases it is made of a metal plate; in others a spiral spring is used, covered with india-rubber to make it steam-tight. The steam-gauge represented by figs. 77 and 78 is the form manufactured by M. B. Edson, of New York.
[39] A _bell-crank_ is a lever with an elbow in it.
[Illustration: Fig. 79.]
[Illustration: Fig. 80.]
In the other class of gauges, shown in fig. 79, the steam acts upon a bent metal tube, _a b c_, usually of a flattened or elliptical section. It may not be known to all readers that if a tube bent, say in the form of the letter ~U~ or ~C~, is subjected to the pressure of a liquid or gas on the inside, the force exerted by the pressure has a tendency to straighten out the tube. This is due to the tendency which a tube of an elliptical or flat section has to change the shape of the latter and approximate to a circular form when the inside is subjected to a pressure. Thus let _A B_, fig. 80, represent a cross section, and _a b d c_, a longitudinal section of a part of such a tube contained between two radii, _O a_ and _O b_, drawn from the centre _O_ of the curve in which the tube is bent. If now we subject the inside of _A B_ to a pressure it will have a tendency to assume the form of the circle _C D_, and would then be represented in the longitudinal section by the dotted lines _a′ b′ d′ c′_. If now we draw radial lines through _a′ c′_ and _b′ d′_, it will be found that they intersect at _O′_, instead of _O_, which was the original centre of the curve of the tube. It will be seen that as the section of the tube approximates to the form of a circle, the portion _a b_ which is outside the curve will be moved farther from the centre, while the other side, _c d_, is moved nearer to it. As indicated by the radial lines, when this occurs either the outside must be lengthened and the inside shortened, to conform to the radial lines _a O_ and _b O_, or else the tube will be straightened so that the radial lines will assume the position _a′ O′_ and _b′ O′_.
The phenomenon of the straightening of the bent tubes of steam gauges is frequently attributed to the difference between the area of the inside and outside of the curve. This error was shared by the writer, until the fallacy of the reasoning which supported it was pointed out to him.
In the gauge represented in fig. 79, (in which the dial-plate is removed), one end, _c_, of the tube is attached at _d_ to a lever which has a toothed segment, _e_, at the other end. The end _a_ of the tube is connected with the lever at _f_. The connection at _d_, therefore, forms the fulcrum of the lever. It is obvious that as the two ends of the bent tube are forced apart by the steam pressure, the lever and the segment have motion imparted to them. The latter gears into a pinion on the spindle of the index or pointer, _r r_, which thus indicates on the dial the degree of pressure in the tube. The latter is connected with the boiler by a tube attached at _g_. Various forms of this kind of steam-gauge are also made, but all act on essentially the same principle.
The position of the steam-gauge on the engine is shown at _M_, in fig. 71.
QUESTION 147. _Why is the pipe which connects the steam-gauge with the boiler bent as shown in fig. 71?_
_Answer._ To prevent the hot steam from coming in contact with the metal plate or tube, as it is found that the heat of the steam affects their elasticity. When a bent tube is used, the steam from the boiler is condensed and fills the bent portion so that when the steam pressure comes on the surface of the water it forces it up the other leg of the tube into the gauge. A cock is attached to this pipe so that the steam can be shut off in case the gauge should get out of order or require to be removed while there is steam in the boiler.
QUESTION 148. _How can the accuracy of a steam-gauge be tested?_
_Answer._ When the gauge is in good working order, the index or pointer moves easily with every change of pressure in the boiler, and if the steam is shut off from the gauge, the index should always go back to 0. In order to determine the accuracy of its indications, however, they should be tested with a column of mercury. This consists of a long, vertical tube, terminating at its base in a closed vessel filled with mercury. The gauge is then attached to the top of this vessel and water or oil is forced into the vessel on top of the mercury and into the gauge. A pressure of one pound per square inch will force up the column of the mercury 2.04 inches, so that by graduating the tube into spaces that distance apart, the divisions will indicate the pressure in pounds per square inch. Thus, a pressure of 50 pounds would force up the column of mercury 102 inches, and with 100 pounds pressure the column would rise 204 inches, and therefore, when the mercury reaches these or any other points, the steam-gauge, if it is accurate, should indicate equivalent pressures.
The ordinary steam-gauges are very liable to get out of order, and therefore they should be frequently tested to ascertain whether their indications are correct.
QUESTION 149. _What is the steam whistle, and for what purpose is it used?_
_Answer._ The _steam-whistle_, _W_, fig. 71, and shown in section on a larger scale in fig. 81, consists of an inverted metal cup or bell, _A_, made usually of brass. The lower edge of this cup is placed immediately over an annular opening, _a a_, from which the steam escapes and strikes the edge of the cup or bell, which produces a deep or shrill sound, according to the size or proportions of the whistle. The annular opening _a a_ is formed by the plate or cover, _a a_, which nearly fills the mouth of the cup _B_, which is attached to the stem _c_. The latter is screwed into the top, _D_, of the dome. Communication with the steam-space of the boiler is either opened or closed by a valve, _b_, which is attached to a sort of spindle, _d_, which extends upward inside of the stem _c_. This spindle does not entirely fill the opening in the stem _c_, so that the steam which enters when the valve _b_ is opened rises and escapes through the holes _e_, _e_, _e_, into the cup _B_ and out through the annular opening _a a_. The valve is opened by the lever _E_, whose fulcrum is at _f_. The end _g_ of this lever is connected by a rod, _h_, figs. 81 and 71, with the cab, and by a suitable handle or lever, _h′ h′_, fig. 71, it can be opened and the whistle be blown at any time by the locomotive runner or fireman to give signals to the trainmen or of the approach of a train to a station, or to warn persons to get off of the track.
[Illustration: Fig. 81. Scale 1¹⁄₂ in. = 1 foot.]
QUESTION 150. _How is a locomotive boiler emptied and cleaned?_
_Answer._ One or two large cocks, called _blow-off_ cocks, _X_, fig. 71, are placed near the bottom of the fire-box, either in front or behind, and sometimes on the side. By opening either of these the water in the boiler is blown out, and much of the loose mud and dirt is carried out with the water. The cock _X_, fig. 71, is opened by a handle, _w_, which is connected with the cock by a rod.
In order to clean out the mud and scale which are not entirely loose, what are called _mud-holes_ or _hand-holes_ are placed in the corners of the fire-box near the bottom. These are oval-shaped holes, about 4¹⁄₂ inches long and 2¹⁄₂ inches wide, and covered with two metal plates, one of which is put inside the boiler and the other outside, and fastened with a bolt through both. Another hand-hole is sometimes placed in the bottom of the front tube-sheet. When the boiler is emptied of water these hand-holes are uncovered, and as much dirt is removed as can be scraped out of these holes. A hose pipe is then inserted and a strong stream of water is forced in, which washes out nearly all the loose dirt, so as to leave the boiler comparatively clean.
When the water is very impure, what is called a _mud-drum_, _M_, fig. 41, is used. Much of the mud and dirt is deposited in this receptacle, from which it can easily be removed by taking off the cast-iron cover on the bottom of the drum. The cover is also provided with a blow-off cock, which is shown in the figure referred to.
QUESTION 151. _What other attachments are there to the boiler of a locomotive?_
_Answer._ There are two cocks, _a_, _a_, fig. 71, called _heater-cocks_, which are connected with pipes to the feed-pipes _D D_, to admit steam to the latter to prevent the water in them from freezing. There is also another cock, _b_, called a _blower-cock_, which is connected to the smoke-stack by a pipe _b_, _b_. Steam is conducted through this pipe and escapes up the chimney in a jet, thus producing a draft when the engine is not working. This arrangement is called a _blower_ and is used to blow the fire when the engine is standing still. The action of the jet is similar to that of the exhaust steam which escapes up the chimney, excepting that the steam from the jet escapes in a continuous stream instead of distinct “puffs,” as it does when it is liberated alternately from one end of the cylinders and then from the other.
_T′_ is a handle which is connected by a rod, _T′ T_, with the feed-cock (not shown in the engraving) in the pipe _D_. This cock can be opened or closed by the handle, and the supply of water fed into the boiler by the pump can thus be regulated. _J_ is a handle on the other side of the engine, for regulating the working of the pump on that side.
_e_, _e_ are handles, also connected by rods with the pet-cocks on the pumps. These cocks can thus be opened or closed, and it can then be known whether the pumps are working.
_A_ is the furnace door, which is fastened by a latch. The latter has a chain, _Q_, attached to it by which it can be conveniently opened or closed. The door also has a circular register with six holes to admit air into the furnace. These holes can be opened or closed by the revolving circular disc shown in the engraving.
[Illustration: Fig. 82. Scale ³⁄₄ in. = 1 foot.]
[Illustration: Fig. 83. Scale ³⁄₄ in. = 1 foot.]
[Illustration: Fig. 84. Scale ³⁄₄ in. = 1 foot.]
QUESTION 152. _How are the grates constructed?_
_Answer._ As has already been explained, they are made usually of cast-iron bars,[40] _A_, _A_, _A_, figs. 82 and 83, called _grate-bars_. Fig. 82 is a plan, and fig. 83 a horizontal section of one form of grate. The bars in this kind of grate are usually cast in pairs, or some times three or more are cast together. They are made wider on the top than on the bottom edges, as shown in the section, fig. 83, so that cinders and ashes will fall through easily, and also to give free access to the air from below. They are usually from ³⁄₄ to 1¹⁄₂ inches wide on the top, and about ³⁄₄ inch on the lower edges. The spaces between the bars are made from ¹⁄₂ to 1¹⁄₄ inches wide. For burning wood the bars are placed comparatively close together and are stationary, but for burning bituminous coal they are usually made so that they can be moved, in order to shake or stir up the fire, just as is necessary in an ordinary stove or grate fire. In the grate we have illustrated the bars, _A_, _A_, are cast in pairs, and run crosswise of the fire-box. The ends are made with a sort of journals, _b_, _b_, which rest on two supports, _B_, _B_, called _bearing bars_, which have suitable indentations to receive the ends of the grate-bars. The latter have arms, _C_, _C_, fig. 83, cast on the under side, to which a bar, _D D_, is attached. By moving this bar back and forth, the grate-bars have a rocking motion imparted to them, as shown in fig. 84. It is evident that in this way the fire over the whole surface of the grates will be disturbed or shaken. The bar, _D D_, is moved by a lever, _m m_, shown in fig. 71. An extension piece, not shown in fig. 71, is used with the lever _m m_, so as to increase its length; but it is removed after it has been used, so as not to be in the way of the fireman. Grates which have movable bars are called _shaking_ or _rocking grates_. A great variety of such grates are made and in use, to describe which would require more room than is available here.
[40] In Europe and in some few cases in this country they are made of wrought iron.
For burning anthracite coal what are called _water-grates_ are used. These consist of wrought-iron tubes, 2 inches in diameter outside, which are fastened in the front and back plates of the fire-box and are inclined upward from the front end, so that there will be a continued circulation of water through them to keep them cool and thus prevent them from being burned out by the intense heat of the fire.
QUESTION 153. _How is the fire removed from the fire-box when it is necessary to do so?_
_Answer._ In bituminous coal burning engines, what is called a _drop-door_, _E E_, figs. 82, 83 and 84, is provided for that purpose. This door is supported partly on journals, _d_, _d_, similar to those in the grate-bars, on which it can turn, and is held up or prevented from dropping by arms, _e_, _e_, attached to a shaft, _F F_. This shaft is operated by a lever, _f f_, fig. 82, outside the fire-box.
When the arms are in the position represented in fig. 83, the drop-door is held up in the place in which it is shown; but when they are turned as in fig. 84, the door falls down so that the burning coal can be taken out of the opening at _G_, and, by raising up the ash-pan damper, _H_, fig. 84, can be raked out on the track or into suitable pits usually provided for this purpose. The drop-doors are sometimes perforated so as to admit air to the fuel on top of them.
The grates for burning anthracite coal usually have about four solid wrought-iron bars between that number of tubes. These bars can be withdrawn, and the fire then falls into the ash-pan through the opening left by the withdrawal of the tubes.
QUESTION 154. _How are the dampers of the ash-pan operated?_
_Answer._ They are connected by suitable rods and levers with two handles, _l_, _l_, fig. 71, which are raised or lowered, thus opening or closing the dampers.