the draught to the wants of the engine. If the pressure becomes very high, the water will be forced out of the boiler through the feeding-valve. This valve, however, is usually made too small to be capable of answering as a safety-valve, but it gives intimation of danger. In steam vessels an upright pipe has been recommended to be applied to the top of the boiler, of sufficient capacity to give free exit to the steam, and descending beneath the water level, so as to be under ordinary circumstances filled with water. When the steam becomes too high, the water is forced up this pipe, and proceeds into the chimney by a branch-pipe provided for the purpose. If the pressure be not speedily relieved, the whole of the water above the mouth of the pipe will leave the boiler, and then the steam will rush out. Another plan consists in the application of a vessel at the end of a lever, to receive the water which flows over from the upright pipe, and this vessel of water is so arranged that its weight opens the safety-valve. In some combinations a column of quicksilver is employed, instead of a column of water; but it has been found that the quicksilver is gradually dissipated by the action of the steam. A large steam-gauge is recommended by some persons as an effectual safeguard against explosion, in the event of an adhesion of the safety-valve; but for all ordinary pressures we think the column of water already described will be found to be a preferable expedient.

Fig. 231.

Slide-valves. There are three principal varieties of slide-valves - the long D, the short D, and the three ported. The long D is represented among the details of the engines of the Clyde, Tweed, Tay, and Teviot steamers, and the three-ported valve is shown in the plates we have given of locomotive engines; but we here again represent it in fig. 231. This valve consists of a box set over a central port, and moved alternately over ports set on each side of the central port, so as to establish a communication between the central and side ports alternately. The central port is the escape port: the steam passes in the direction of the arrows, and when exhaustion is being performed by one port, steam is being admitted by the other. This species of valve is used very extensively in high-pressure engines, and almost universally in locomotives. It is very simple; and by leaving the face of the cylinder when the pressure within the cylinder exceeds the pressure in the valve-casing, it enables the water to escape when the engine primes: but it occasions a considerable waste of steam if the ports and passages are large; and if they are not large, a considerable loss of power arises from the extra-resistance experienced by the piston.

The long D valve has always been in much favour with engineers, though, as we think, without sufficient reason. The short D valve, is in our judgFig. 232.

ment, preferable, and we give in fig. 232, an excellent specimen of this species of valve-the valve of the steamer Don Juan. Some short D valves have only one rod to connect the ends, and others have two; but three are preferable, as they give greater stiffness than is otherwise attainable. It is expedient to zine the connecting-rods, as in the wake of the ports they frequently get wasted rapidly away by the steam.

The piston-valve with skewed ports is represented in fig. 233. This species of valve is, in our judgment, preferable to the D in many respects. It is more easily worked, admits of metallic packing, and is not liable to have its form altered by twisting. Messrs. Miller, Ravenhill, and Co., have adopted this species of valve in their oscillating engines of the largest size, but in this instance its operation has not been satisfactory.

In working large engines considerable difficulty is experienced in handling the valves, from the weight

Fig. 233.

PISTON VALVE.

and the pressure of the steam forcing the valve against the face of the cylinder. Various schemes have been adopted to obviate this disadvantage. In some cases a small engine has been used to work the valves at starting, and another plan has been to balance the valves by the opposing pressure of the steam. One of these balance valves is represented in figures 234, 235, and 236. It is a slide-valve, and has no hemp packing as is usual, but is kept tight by means of a metallic packing-ring, divided into segments which are pressed against the inner side of the valve-chest back by spiral springs and steam pressure. Some inconvenience might be anticipated from the circumstance of the rubbing surface of the packingring at the sides of the valve being greater than at the ends: but we understand from Messrs. Rennie, by whom this valve was devised, that its performance has been found satisfactory.

2.11

4.0

A

SLIDE-VALVE OF DON JUAN STEAMER.

Back View.

EQUILIBRIUM SLIDE-VALVE, BY MESSRS. RENNIE.

a a a is a brass ring divided into segments, as shown in the plan, the object being to allow the ring to accommodate itself to any slight curve that may be caused by the pressure of steam on the valve-box back or cover. bbbb is a space containing about three layers of well-plaited square gasket. cccc is a brass ring in one piece fitted loosely into the groove, having on one side of it a number of small steel pegs, d d d d, on which is

11 2

be turned round upon it, and thus give the required lead. Fig. 238. represents the variable expansive gear of Mayer. It consists of an ordinary valve, with the addition of perforations through the top and bottom faces, each of which are covered by a supplementary valve upon the back of the first, consisting of two solid blocks, into which a valve rod is screwed, having a right-handed screw where it penetrates the one block, and a lefthanded screw where it penetrates the other; so that the blocks will be set closer or further apart, according to the direction in which the rod is turned. The ordinary valve receives its motion in the usual way, and the expansionvalve is moved by means of a pin attached to the piston-rod, which works in a slotted lever, to which the expansion-valve rod is attached. motion of the two valves is, therefore, at right angles, and the expansionvalve is about one-fourth of a revolution in advance of the steam-valve. In the figure, A is the steam-valve, BB the expansion-valve, TT the valve rod, with right and left handed screw; G a wheel attached to the valve rod, over which a pitch chain passes, by means of which the valve rod is turned, and the blocks are altered so as to give the requisite amount of expansion; D is the valve shaft, and CE the valve lever; F is the pin attached to the piston rod. In all cases in which the motion of the expansion-valve is the same as that of the piston, the slide-valve must be provided with lap.

The

The expansion of the American engines is, as shown in the engine figured in page 190, generally a disk turning upon an axis like a throttlevalve, but so made as to be capable of being turned completely round in the pipe. The expansion-valve of the Don Juan was of this description, and was worked from a pin in a pinion, which made two turns for each revolution of the engine. In Mr. James Whitelaw's expansion-valve the valve shaft is cranked slightly, so as to enable the end of a double-ended lever to be in the centre line of the shaft, the centre of this lever being supported by a pin passing through the valve levers, and the expansionvalve, which consists of a plate placed between the valve and cylinder faces, is hung from the other extremity. So long as the end of the lever which is situated in the central line of the valve shaft, is preserved stationary, the expansion-valve has the same motion as the other valve, or is relatively at rest, so that no expansion then takes place; but if the end referred to of the lever be moved, as is done by means of a suitable cam upon the shaft, expansion answerable to the degree of motion is then accomplished. Some expansion-valves are gridiron valves, or valves consisting of a great number of ports instead of one, whereby the extent of travel necessary for their action is diminished. Mr. Bourne has introduced into some steam vessels a species of expansion-valve which cuts off the

steam close to the valve face, so as to prevent expansion in the valvecasing, and is easily applicable to existing engines. It consists of two plates, moving between the valve tails of the D valve, and shutting up against the lap. These plates are connected together by a rod, and motion is given to them by means of a suitable cam or tappet: for moderate rates of expansion the motion given by a tumbler will suffice. In engines with a considerable amount of lap upon the valve, the amount of expansion will be increased by partially closing the throttle-valve, and in such cases the use of an expansion-valve in the steam-pipe cannot be productive of much benefit. This effect is traceable to the quicker motion of the piston in the cylinder as it approaches the centre of the stroke; for a size of orifice that will admit steam enough to keep up the pressure at the beginning of the stroke, when the motion is very slow, will not do so when the motion quickens, and the pressure necessarily subsides within the cylinder. If, however, there be no lap upon the valve, the pressure within the cylinder will rise towards the end of the stroke, when the motion again becomes slow; but if there be lap upon the valve sufficient to prevent the steam from entering towards the latter part of the stroke, the steam may be very largely expanded in the cylinder by throttling in the steam pipe. To make the action satisfactory, however, the throttling of the steam should take place close to the steam port; and one of Mr. Bourne's arrangements consists of a moveable plate covering holes upon the steam side of the valve, through which holes the steam finds ingress into the cylinder. These moveable plates are not made to travel at every stroke of the valve, as in the case of common expansion valves, but are moved by means of a rod passing through a hollow valve, spindle or otherwise, merely, whenever the rate of expansion requires to be changed; and the extent to which the steam orifices are open determines the extent of the expansion. The valve is made with sufficient lap to cut off the steam when about two thirds of the stroke have been performed, and with these proportions, and with the steam orifices very much contracted, the expansion begins very near the beginning of the stroke, and continues down uninterruptedly to its close. This species of expansion valve appears to be the best for locomotive engines, and for all engines, indeed, travelling at a quick speed, to which species of engine the spindle expansion valves are inapplicable. The moveable plates may obviously be used as a throttle valve, and the steam, by their instrumentality, may be completely shut off without throwing the engine out of gear. In all cases in which there is much lap upon the valve, it is expedient to make the throw of the valve more than twice the depth of the ports; as the orifice of the eduction passage will otherwise be too much contracted.

THE PUMPING-ENGINE.

IN a pamphlet printed by Messrs. Boulton and Watt, for the use of their servants, sometime between 1782 and 1785, we have some excellent practical directions respecting the construction and management of pumpingengines, the greater part of which are applicable to the circumstances of the present time. This pamphlet is now very scarce; but we have been favoured by Messrs. Boulton and Watt with the use of a copy, and propose here to insert the most valuable part of its contents. Mr. Watt's hand is visible enough in this production, and the highest praise we can give to it is to say that it is worthy of its author. Under the head of general directions we have the following:

"Having fixed upon the proper situation of the pump in the pit, from its centre measure out the distance to the centre of the cylinder, that is the length of the working-beam, or great lever, and the half breadth of each of the great chains, as shown by the drawing. Then from the centre of the cylinder set off all the other dimensions of the house, including the thickness of the walls, and dig out the whole ground included (to the depth of the bottom of the cellar) so that the bottom of the cylinder may stand on a level with the natural ground of the place, or lower, if convenient, for the less height the house has above ground, so much the firmer will it be. The foundations of the walls must be laid at least two feet lower than the bottom of the cellar, unless the foundation be firm rock, and care must be taken to leave a small open drain into the pit quite through the lowest part of the foundation of the lever wall, to let off any water that may accidentally be spilt in the engine-house, or may naturally come into the cellar. If the foundation at that depth does not prove good, you must either go down to a better, if in your reach, or make it good by a platform of wood or piles, or both.

"The foundation of the lever wall must be carried down lower than the bottom of the space left under the condenser cistern (to get at the screws which fix the condenser), and two short walls must be built to carry the beams under the condenser cistern. Two other slight walls should be built, one on each side, at a little distance from that cistern, to keep the earth from it, which would otherwise cause it to rot.

"Within the house, low walls must be firmly built to carry the lower cylinder beams, so as to leave sufficient room to come at the holding-down screws, as shown in the drawing, and the ends of these beams must also be lodged in the wall, but the platform is not to be built on them until the house is otherwise finished.

"The lever wall must be built in the firmest manner, and run solid, course by course, with thin lime mortar, and care must be taken that the lime has not been long slacked. If the house be built of stone, let the stones be long and large, and let many headers be laid through the wall; it should also be a rule, that every stone be laid on the broadest bed it has, and never set on its edge. A course or two above the lintel of the door which leads to the condenser, build in the wall two parallel, flat, thin bars of iron equally distant from each other, and from the outside and inside of the wall, and reaching the whole breadth of the lever wall. About a foot higher in the wall, lay at every four feet of the breadth of the front, other bars of the same kind at right angles to the former course, and reaching quite through the thickness of the wall, and at each front corner lay a long bar, in the middle of the side walls, and reaching quite through the front wall. If these bars are 10 or 12 feet long, it will be sufficient. When the house is built up nearly to the bottom of the opening under the great beam, another double course of bars are to be built in, as has been directed.

"At the level of the upper cylinder beams, holes must be left in the walls for their ends, with room to move them laterally, so that the cylinder may be got in, and smaller holes must be left quite through the walls, for the introduction of iron bars; which being firmly fastened to the cylinder beams at one end, and screwed at the other or outer end, will serve by their going through both the front and back walls, to bind the house more firmly together.

“The spring beams, or iron bars fastened firmly to them, must reach quite

through the back wall, and be keyed or screwed up tight, and they must be firmly fastened to the lever wall on each side, either by iron bars, firm pieces of wood, or long strong stones reaching far back into the wall; they must also be bedded solidly, and the sides of the opening built in the firmest manner with wood or stone. The spring beams must always be laid eight inches on each side distant from the working beam, to give room for the side arches.

"The house being finished, a wooden platform of 24 inch plank, is to be laid on the lower cylinder beams, and the centre of the cylinder being accurately marked on it, four holes are to be bored through the cylinder beams, for the holding-down screws, and four boxes, about seven or eight inches square, and as long as the stone platform is to be deep, are to be placed perpendicularly over them. Then the stone or brick platform is to be built up to the level of the cylinder's bottom, as shown in the drawing; it must be composed of the heaviest materials which can readily and cheaply be procured. A very solid pillar of stone or brick work, laid in the best lime mortar, must be carried up directly under the cylinder, and must be, at least, of the diameter of the outside of the flanches; the rest of the platform may be filled up with the heavy materials, bedded solidly in a mortar of clay and sand, and well beat into their places, so as never to settle or yield."

We next have some excellent remarks upon the construction of boilers, and upon boiler-setting :

"In making the boiler you should use rivets between five eighths and three fourths inch diameter. In the bottom and sides the heads of the rivets should be large and placed next the fire, or on the outside, and in the boiler top the heads should be on the inside. The rivets should be placed at two inches distant from the centre of one rivet to the centre of the other, and their centres should be about one inch distant from the edge of the plate. The edges of the plates should be evenly cut to a line, both outside and inside. It is impossible to make a boiler top truly tight which is done otherwise. After the boiler is all put together, the edges of the plates should be thickened up, and made close by a blunt chisel about a quarter inch thick in the edge impelled by a hammer of three or more pounds weight, one man holding and moving the chisel gradually, while another strikes. All the joints above water should be wetted with a solution of sal amoniac in water, or rather in urine, which, by rusting them, will help to make them steam tight. After the boiler is set, it may be dried by a small fire under it, and every joint and rivet above water painted over with thin putty, made with whiting and linseed oil, applied with a brush. A gentle fire must be continued until the putty becomes quite hard, so as scarcely to be capable of being scratched off by the thumb nail, but care must be taken not to burn the putty, nor to leave off fire until it become dry.

"In building the brick-work of the boiler-setting, no lime must be used where the fire or flame comes, but a mortar made of loam or sand and clay; but lime mortar should be used towards the outside. Pieces of old cart tire, or other such like pieces of iron, may be laid under the chime of the boiler, between it and the bricks, which will prevent its being so soon burnt out there. The brick-work which covers the boiler top should be laid in the best lime, which will not hurt it there, but will preserve it; the mortar should be used thin, and the boiler top well plastered with it, which will conduce greatly to tightness, if done some time before the engine be set to work. If your lime be not of that species which stands water, it will be well to mix some Dutch or Italian terrass, or pan scratch from the salt works with it, but in any case the lime should be newly slacked. In carrying up the brick-work round the flues, long pieces of rolled iron should be built in two or three courses to prevent the brick-work from splitting. Four holes at convenient places should be made into the flues, large enough to admit a boy to go in to clean them. One of them may be over the fire door, and another right behind the damper in the back side of the chimney. This last may be as high as the flues themselves are. These holes, when not in use, are to be built up with nine-inch brick-work, and made perfectly air tight. Immediately above the brick-work of the boiler-setting, a hole

must be left in the chimney on the side next the boiler. This hole must be as wide as the chimney, and one foot or 18 inches high, and must have a sliding door fitted to it, to open it more or less at pleasure; the use of it is to moderate the draught of the chimney, and to prevent the flame being drawn up it before it has acted sufficiently on the boiler. A groove must be left in the brick-work for the damper to move up and down in easily, which should fit flat to the face of it. The damper may be made to move easily up and down by means of a beam or a wheel, with a counterpoise equal to the weight of the damper. The best form of a fire door is two feet long and one foot high, inside measure, to have two leaves made of boilerplates hinged on the two sides, and over-lapping one another about an inch in the midlde. The scantling of the frame may be three inches broad by two inches thick."

We have next some directions respecting the formation of a refrigeratory pond for the hot water. Throwing the water up into the air in the form of a jet to cool it was found to be detrimental, as it charged the water with air, which vitiated the vacuum:

"If you have not land water that will naturally run into the condensercistern, you must make a pool somewhere in the neighbourhood to receive the water from the hot-water pump, and reserve it for supplying the boiler and condenser-cistern when the engine stands still on any occasion. This pool may be at least 40 feet long, and 20 feet wide, to hold 3 feet deep of water; and pipes or troughs must be laid from its bottom to the boiler, feed-pipe, and to the cistern. That at the feed-pipe must have a cock on purpose. It is only meant that this pool be simply dug in the earth and lined with turf, puddled, or otherwise made water-tight. If no ground within a reasonable distance be high enough for the water to run from the bottom of the pool into the boiler, then a pool may be made on lower ground, and a hand-pump fixed up to supply the boiler and cistern; but this ought to be avoided if possible."

Next come some directions for putting the engine together:"Having put the working-beam together, and fastened the gudgeon to it, rest it on the plummer blocks; but do not fasten these blocks until the cylinder is fixed.

"Level the top of the stone platform, and lay the outer bottom of the cylinder down in its place, truly level, and corresponding to the holdingdown screw-boxes.

46

Apply the inner bottom upon the outer one, and set its upper joint level, by wedging betwixt it and the outer bottom if it requires it: then cut out segments of pasteboard, such as is used for the boards of books (not such as is composed of paper pasted together); let these segments be of such thicknesses as the different parts of the joint may require (if it be more open in some places than in others). Soak these pasteboard segments in warm water until they become quite soft, then lay them upon boards to dry, and when quite dry put them into a flat pan with a quantity of drying linseed oil; warm the oil until the pasteboard ceases to emit bubbles of air, but take care not to heat the oil much hotter than boiling water, otherwise it will harden or burn the pasteboard. Anoint the segments on both sides with thin putty made with fine whiting and some of the linseed oil; let the whiting be very dry, otherwise it will be difficult to mix with the oil, and N. B. that white lead will not answer in place of it.

"You must, as much as you can, avoid using more than one thickness of pasteboard, and the segments should be a little broader than the flanch, with all the holes cut out by a chisel, but not quite so large as the holes in the iron. The segments should also be thinned at the ends where they overlap each other, so that they may form a circle of pasteboard of an uniform thickness.

"To pack the piston, take sixty common-sized white or untarred ropeyarns, and with them plait a gasket or flat rope, as close and firm as possible, tapering for 18 inches at each end, and long enough to go round the piston, and overlap for that length; coil this rope the thin way as hard as you can, lay it on an iron plate, and beat it with a sledge hammer until its breadth answers its place; put it in and beat it down with a wooden driver and a hand-mallet; pour some melted tallow all round; then pack in a layer of white oakum half an inch thick, then another rope, then more oakum, so that the whole packing may have the depth of about four inches, or only three inches if the engine be a small one. Cast segments of a circle of lead, about 12 inches long, 3 inches deep, and 14 inch thick, fitted to the circle of the piston, and cut down square at both ends; lay them round upon the packing as close as they can lie to one another without jamming, and screw down the piston springs upon them; the piston springs should be bent downwards at the end next the piston-rod, and a little mortoise should be cut in the cast-iron there, for the bent-down point of each of them to lodge in, which will prevent their coming forwards to touch the cylinder. Previous to the piston being put into the cylinder, the hollows among the crosses should be quite filled up with solid pieces of deal wood, put in radius fashion. The packing of the piston should be beat solid, but not too hard, otherwise it will create so great a friction as to hinder the easy going of the engine. Abundance of tallow should be allowed it, especially at first; the quantity required will be less as the cylinder grows smooth.

"The joints being all made, the regulator valves in their places, and their covers screwed on, but no water in the condenser cistern, admit steam, and when the cylinder and steam case are thoroughly warmed, screw up the nuts of all your screws, and caulk the pasteboard or oakum of such

joints as may require it, with a caulking chisel, until you find that every thing about the cylinder is perfectly staunch; then pour three or four feet deep of water into the hot-water pump; stake down the injection and blowing valves, and also those on the air-pump lid; then let the steam into the condenser, which will show the defects or leaks, if there be any.

"Screw on the steam gauge to the steam case near the nozzle, and behind the engine-man's place; pour as much mercury into it as will half fill the open leg; put a float on it, broad at bottom, but very slender in the stem; cut the float or index off close to the end of the open tube, and fix a scale to it, reckoning every half inch the float rises equal to an augmentation of the elasticity of the steam, corresponding to the supporting of a column of mercury an inch high, because the surface has sunk as much in the one leg as it has risen in the other. Solder a small copper fosset-pipe, to fit the copper communicating tube of the barometer, into the eduction-pipe, 12 inches under the fosset of the blowing valve, and on the opposite side of the eduction-pipe; place the barometer in the door-way to the condenser on the further side from the plug-tree, so that the engine-man may see it when at his station; join the copper tube to it by pouring melted sealing-wax into the copper cup at top; fill the short leg of the barometer with mercury, within four or five inches of its top, and put a light float in it, long enough to reach to the top of its frame.

"Fill the condenser cistern, shut the lower regulator, and there being no steam in the cylinder, or its communication with the boiler being cut off, take off the bonnet or cover of the exhaustion regulator, shut that regulator, and work the air-pump by means of the brake. If then you find that air enters by the regulator, pour some water on it, and continue pumping until you have raised the barometer, i. e. sunk its float, to 27 or 28 inches; leave off pumping, and observe if the vacuum continues good, or is a long time in being destroyed, If it looses fast, seek for the leaks, which must be somewhere in the eduction-pipe, and will make a noise if touched with a wet hand (observe if the condenser moves by the pumping, and secure it). After having cured these leaks, you may try the tightness of the cylinder by staking the working-beam, so that the piston cannot descend; then taking the cover off the cylinder, open the exhaustion regulator, and shut the steam regulator; on beginning to pump, you will perceive if the piston be tight; if it is not, it may be beat a little, and some water being thrown upon it, and on the steam regulator, whatever air enters must be by leaks, which must be sought for and cured by screwing or caulking in oakum. "N. B. A critical tightness in the piston cannot be obtained until the engine has gone a few days, without beating it too hard, to permit the engine to move easily. When you can detect no more leaks in this way, the steam must be admitted, and the same examination made as before. "After the engine has been set a-going, and has gone a few hours, the holding-down screws should be screwed tight, and so from time to time as they become slack; and in like manner all the other screws about the cylinder or nozzles should be screwed up as they slacken, and the joints caulked and puttied where they require it.

We have next directions for working the engine:

"To set the engine a-going, raise the steam until the index of the steam gauge comes to three inches on the scale; when the outer cylinder is fully warmed, and steam issues freely on opening the small valve at the bottom of the siphon or waste-pipe, which discharges the condensed water from the outer bottom, open all the regulators; the steam will then forcibly blow out the air or water contained in the eduction-pipe, by the blowing-valve, but cannot immediately take place if the air is in the cylinder itself; to get quit of it, after you have blown the engine a few minutes, shut the steam regulator; the cold water of the condenser cistern will condense some of the steam contained in the eduction-pipe, and its place will be supplied by some of the air from the cylinder; open the steam regulator and blow out that air; and repeat the operation until you judge the cylinder to be cleared of air; when that is the case, shut all the regulators, and observe if the barometer shows that there is any vacuum in the eduction-pipe; when the barometer gauge has sunk three inches, open the injection a very little, and shut it again immediately; if this produces any considerable degree of vacuum, open the exhaustion regulator a very little way, and the injection at the same time; if the engine does not commence its motion, it must be blown again, and the same operation repeated until it moves; if the engine be very lightly loaded, or if there is no water in the pumps, you must be very nimble and shut the exhaustion and top regulators, so soon as it begins to move quickly, otherwise it will make its stroke with great violence, and perhaps do some mischief. To prevent which, open the top and exhaustion regulators only a little way, and put pegs in the plug-tree, so that they may be sure to shut these regulators long before the piston comes to the bottom.

"If there is much unbalanced weight on the pump-end, you must also take care to put a peg in the ladder which guards the steam-regulator lever, so as to allow that regulator to open only a little way, and so to lessen the passage for the steam, when it enters to fill the cylinder, otherwise the rods, &c., at the pump-end may descend too fast and be prejudicial; if you find, after a few strokes, that the engine goes out too slow, the steam-regulator may be opened wider. In order to regulate the opening of the exhaustion regulator, you should have pieces of board, of various thicknesses, to put under the weight which pulls it open, by means of which it may be made to open more or less at pleasure, and the top regulator may be managed in the same manner.