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.

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.

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.

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.

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.

LIST OF PARTS DESIGNATED BY LETTERS OF REFERENCE IN FIG. 71.

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.

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.

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.

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.

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:

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]

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.

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.

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.