The automatic governor is located on the shaft, between the cranks, and actuates the valve direct without rock-shafts or other mechanism.
The Westinghouse Compound Engine is similar in general characteristics to the non-com pound engine above described. It is shown in section in Fig. 60. One cylinder is enlarged to practically three times the area of the other. The valve-chest is across the top of the cylinders, and is in one piece, the various steam-passages be ing chambered in it. The valve-seat is in the form of a bush, in which the ports are cut to an exact register. This bushing is reamed out and forced steam-tight into its bored seat.
The valve-chest also contains a small by-pass valve controlling a cored passage, by which live steam can be admitted to the low-pressure cylinder, to turn the engine over its center when starting. The steam and exhaust connections, are on the side of the valve-chest toward the back of the engine. The valve is actuated by a single eccentric con trolled by a shaft-governor, shown in Fig. 61. It is inclosed in a case which is tilled with oil when the engine is first set up, and requires no further at tention for an indefinite period. The eccentric alone is outside of the governor-case, being carried on a shaft running through a sleeve, and bearing against stops when at full throw.
The economy of steam of the Westinghouse engines is shown in the following figures published by the builders. The first table gives the results of three tests of a non-compound 45 horse-power engine, under three conditions of loading: The next table shows the results of tests made in 1888 of a compound engine 14 and 24 in. cylinder, 14-in. stroke, under varying loads. The engine was unjacketed. The steam was measured after being condensed in a surface-condenser, which was less open to the atmosphere in the non-condensing tests. The steam consumption is given in pounds per indicated horse power per hour : • The IVillans Triple-Expansion Engine, made by Winans & Robinson, Thames-Ditton. England, is shown in section in Fig. 62. The piston-valve is shown at the left of the engine.
The engine is arrancred with the high-pressure cylinder above the intermediate cylinder, and with the latter the low-pressure. In engines which have more than one crank, each crank is surmounted by a complete engine, all the pistons of which are carried by one piston-rod. The rod is of large diameter and is hollow, and the valve for admitting and
exhausting the steam from the several cylinders works up and down inside it, in the center of the engine (hence the name " central-valve "). It is driven in the usual way by an eccentric, but. since the valve-face (i. e., the inner surface of the hollow rod) moves up and down with the pistons, the source of the valve-motion (i. e., the eccentric) must move up and down with the pistons also. This is effected by mounting the eccentric on the crank-pin, instead of on the shaft, as usual. The ports through which the steam enters and leaves the respective cylinders are simply holes in the hollow rod. These are exposed alternately to steam' coining from above, through the rod, and to exhaust (also through the rod) downward, according as the corresponding pis tons of the valve pass below the holes or above them. Steam enters at the top, through the gov ernor throttle-valve, shown in section, into the steam-chest. The top of the hollow rod, though uncovered, is closed against the steam by the upper most piston of the valve, which works in the part above the holes. Steam can therefore enter the rod only when the holes are in the steam-chest, as they are when the high-pressure piston is neer the upper part of its travel. On commencing t he down stroke the uppermost valve-piston is just passing below the holes, and therefore admits steam into the first or high-pressure cylinder. It rises again, and closes the ports, when the piston has descended about three quarters of its stroke; but the cut-off is effected earlier than this by the holes in the upper part of the hollow rod, leaving the steam-chest and passing through the gland in the cylinder-cover thus losing their supply of steam. It is evident that. the cut-off may be made to take Idece at any part of the stroke, merely by drilling the holes high er or lower in the rod ; the lower they are the earlier in the stroke will they leave the steam-chest. (The same effect is produced by altering the height of the gland in the evlinder-cover.) After cut-off, the .