with its valve, and an elevation of the necessary gearing for working the steam and expansion valves. Fig. 2, is an elevation of the gear

The cylinders are

provided, in the usual way, with pistons, piston-rods, and connecting

rods, for the purpose of communicating the power of the steam to two cranks at right angles to each other on the same shaft, or axle, to which the driving wheels of the engine are attached. The steam from the boiler enters through the pipe, A, into the valve-box, B, which box contains two flat sliding valves, I and K, attached to the same rod, 3, for the purpose of cutting off the communication between the boiler and the cylinder, so that the steam may act on the piston by its expansive force. The two valves, I and K, have nuts let into them, one with a right-handed, and the other a left-handed thread, into which the rod, 3, is screwed, so that when it is turned, by means of the endless screw, 50, and wheel, 51, the distance between the valves is either increased, or lessened, according to the degree of expansion required. At the end of the rod on which is fixed the endless screw, 50, a fine thead is cut, with a traveling index, which shows the precise amount of expansion. The rod, 3, is connected to the lever, 4, by means of another rod, 5, and the lever, 4, is attached to a shaft, 6, on which is fixed another lever, 7, which receives motion from the eccentric, S, through the eccentric rod, 9 9. The eccentric rod, 99, can be made either to impart its motion to the lever, 7, as represented in the drawing, or by raising it by the lever, 10, and link, 11, to the lever, 12, which is fixed on the shaft, 13. The eccentric, 8, is fixed on the main crank-shaft of the engine in such a position that its centre, 15, may make an angle of 45° with a line drawn from the centre of either of the pins, 16 or 17, through the centre of the main shaft, 14, when the piston is at the top of its stroke. C to G, and H H, are two piston-valves, connected by the rod, X, having passages, 22 and 23, through which the steam passes from the openings, C and D, and alternately to each side of the piston, 18, and Fig. 2.

27

28

45

thence through the openings, 20 and 21, into the eduction passage, 24, and blast pipe, 25, whence it finally escapes into the atmosphere, after having performed its duty in the cylinder. These valves are connected to the lever 1, by the rods Y Z, which lever is fixed on the weigh-shaft 2, to which are also fixed two levers, 22 and 23, which receive motion from the eccentric L, by means of the eccentric rod M, which terminates in two forks, N N1, and a slot, O. The eccentric L, is fixed on the crank-shaft, 14, at an angle of 90°, with a line drawn from the centre of the crank-shaft 14, to the centre of the weigh-shaft 2, when the piston is at the top of its stroke. The

forks of N N1, serve to guide the pins R and S, into their respective notches in the usual way, when the engine is reversed, or the contrary. A roller, P, is placed in the slot O, and turns freely on a pin at the end of the lever Q, which supports the weight of the eccentric rod M, and shifts it either on to the pin R, or the pin S, according to which way the engine is required to move. This lever, Q, is fixed on the lifting shaft W, which receives its motion from the lever T, connected by the rod U, to the reversing lever, which is under the control of the driver. The gear for working the valves of the second cylinder, represented in fig. 2, differs but little from the gear employed to work the other. The eccentrics 26 and 27, are placed in a similar position as the eccentrics 8 and L, before described, and the eccentric rod 28, is similar, in every respect, to the eccentric rod M, and communicates its motion to two levers, 29 and 30, on the weigh-shaft 31, to which the lever 32, is fixed, which gives motion to the slides, similar to G and H, fig. 1, through the rod 45, in the same way as before described.

The rod 3, which is fixed to slides similar to I K, in fig. 1, receives its motion from a lever, 35, fixed on the weigh-shaft 13, on which is another lever, 36, to which the eccentric 27, gives its motion through the rod 37. The eccentric rod 37, can also be made to impart its motion to the lever 38, on the shaft 6, by lifting it up, the fork 47, guiding the pin 44, into the notch provided for it. The levers, rods, &c., are shown in such a position as to make the cranks and shaft revolve in the direction shown by the arrows. But when it is required to reverse the motion of the engines, the rod U, is moved by means of the reversing lever V, in the direction indicated by the arrow, causing the lever T, to turn the shaft W, on its centre. The motion thus communicated to W, passes down the levers Q, 39 and 40. The lever Q, causes the rods M and 28, to move off the respective pins, R and 30, on to the pins S and 29, thereby reversing the steam-slides G and H, and similar ones in the other cylinder. At the same time the small levers 39 and 40, cause the levers 10 and 41, to move about their respective centres, 43 and 42, and thereby the eccentric rods 9 9, and 37, to move off the pins 16 and 36, on to the pins 17 and 44. It will be seen that by this arrangement the eccentric 8, will work the expansion-slides of the opposite engine, and vice versa, thereby reversing the expansive-slides of each cylinder. The valves I and K, may be made either in one piece, or two; but Mr. Parsons prefers making them in two, for the purpose of adjusting the expansion to any required degree. To keep the steam warm during its action in the cylinder, he uses a jacket, 45, and allows the steam from the boiler to have free access to the space between it and the cylinder, and likewise to the spaces 46 and 47, at the top and bottom of the cylinder. Mr. Parsons recommends that the whole of the jackets and steam spaces shall be well clothed with felt.

The description given in the specification of this arrangement, for working and reversing the expansive valves, concludes with a valuable suggestion: "It may be applied," says Mr. Parsons, “to work the ordinary valves of locomotive engines, when the lead of the

eccentrics amounts to an angle of 45°, whereby two of the four eccentrics, now generally employed, may be dispensed with."

The metallic packing for the pistons and valves is constructed in a novel and very ingenious manner: two split rings made of any two metals, such as wrought and cast-iron, which expand unequally under equal increments of temperature, are riveted, or otherwise firmly secured together, the most expansive metal being placed innermost. The splits in the two rings do not correspond, but are made at a short distance from each other, so that the inner ring shall extend behind a tongue, which is accurately fitted into the outside ring, by which means the steam is prevented from passing through the splits when the rings become heated by the steam. The inner one expanding more than the outer, they have a natural tendency to open, or buckle outwards, and press against the cylinder without the aid of springs; and this property they will retain until the outside ring is completely worn away. The pressure too must always be in proportion to the temperature, and, consequently, the pressure of the steam. In the valves, the outside ring is made to lap over the edges of the piston frames, which, consequently, do not interfere with the passages.

Ibid.

On working Locomotive Engines Expansively, and the applicability to the purpose of Parsons' Patent Expansive Apparatus. By Messrs. PARSONS and BUNNING, Civ. Engs.

Many attempts have been made to effect a saving of fuel in locomotives, by working the engines more expansively than is now the practice, but experience has seemingly proved that no advantages are gained by making the steam expand more than one-fourth of the stroke. Many engineers have attributed the failure to the rapid rate the engines travel at, which, they think, does not allow time for the steam to expand. But this reason cannot hold good; for when the steam is once admitted into the cylinder, cut off and confined there, were it not to expand, it must be at a greater pressure near the cover of the cylinder, than near the piston, which is manifestly absurd. Doubtless, however, there is a loss which a common unexpansive engine is liable to, from the great velocity of its piston; for when the crank is going over its centres, the piston has scarcely any motion, and the steam has time to pass through the openings, and attain a pressure nearly equal to that in the boiler. But the very great velocity of the piston, when at half-stroke, considerably reduces the pressure in the cylinder, which, however, is again increased as the piston loses its velocity, so that the whole cylinder, full of 50 lb. steam, is used, while an average pressure of perhaps from 40 to 45 lbs. only is rendered available. This is manifestly occasioned by the openings into the cylinder being too small to supply steam, when the piston is moving at its greatest velocity. But this loss will not attend an engine in which the steam is cut off before the piston has attained that

greatest velocity; for the steam, once in the cylinder, cannot be throttled, it is a mechanical impossibility that it should not expand.

The great drawback, however, to expansion with the common slides, is most probably the loss of power occasioned by closing the eduction opening too soon, and thereby compressing the steam that remains in the cylinder; for, suppose the steam is cut off at half stroke, admitted precisely as the piston is at one end of the stroke, and allowed to pass into the atmosphere at the moment it arrives at the other, then it is evident that the eduction port will be closed, and the communication with the atmosphere cut off at half-stroke. Now, although this does not seem a very great evil at first sight, as the steam is supposed to have been already got rid of, yet it is a source of a most serious loss of power. For the back pressure on a locomotive, owing to the diminished size of the blast-pipe, is certainly not less than 5 lbs. per inch, and the pressure of the atmosphere being 15 lbs., makes a total pressure resisting the force of the steam equal to 20 lbs. per inch, at the time the communication with the atmosphere is shut off. Let us suppose, therefore, that the cylinder has a 20-inch stroke; the back pressure being, as we have shown, 20 lbs., when the piston has traveled 10 inches, and, consequently, when it has moved another 5 in. the pressure will be increased to 10 in. of 20 lb. steam, compressed into 5 in., which would be equal to 40 lbs.; and at the end of the stroke it will equal 5 in. of 40 lbs. steam, compressed into the clearance, say half an inch, or not less than 400 lbs. upon the inch; but when the total pressure of this steam on the face of the valve which covers the opening, exceeds that on the back, it lifts the valve, and allows the steam from the boiler a free communication with the atmosphere. This, then, is the reason of the non-success of expansion, when carried to any considerable extent with the common valve, and not, as supposed by some, because the steam has not sufficient time to expand.

It is usual with the best engine makers to allow the steam to pass into the atmosphere, a little before the piston has arrived at the end of its stroke, and it is undoubtedly advantageous to do so, as by that means the eduction port is well opened by the time the piston begins to return; but if this is carried too far, there is a loss of power, as the steam is thrown away before it has given out the whole of its force.

Expansion with the common slide, (to be attended with beneficial results,) is, therefore, limited; for if carried beyond a certain extent. the loss, from throwing away the steam before the piston has arrived at the end of its stroke, and from compressing it in the cylinder more than counterbalances the benefits derived from the increased expansion. It, therefore, becomes a nice point to settle how to obtain the greatest quantity of expansion without diminishing the power of the engine. Experience and the practice of the most celebrated makers have proved, that the best and most economical point at which to cut off the steam with the common slide, is at about three-fourths of the stroke of the piston. If carried beyond this, the evils above enumerated, begin to manifest themselves; but in our patent engines, with our patent apparatus, the steam may be cut off at any part of the