Fig. 252.
Assume that the piston is in position shown, [Fig. 253], and that both the main and auxiliary valves cover their respective steam ports. By means of a starting bar, operating through a stuffing-box in the valve chest, the piston valve, A, is moved toward the head of the steam chest, D, thus opening the ports, E and L, and admitting live steam through L, from the cavities, S, of the valve piston to the housing end of the main steam cylinder, through the port, F, [Fig. 255], forcing the main piston, P, toward the opposite end of the stroke, or toward the left in the figure. The port, E, [Fig. 253], being open, the exhaust steam escapes from front of the main piston through the port, F, [Fig. 255], into the main exhaust port, G, through the port, E. The piston, P, travels to its extreme left position and the auxiliary slide valve has been drawn to such a position in the direction indicated by the arrow in the smaller drawing in [Fig. 252], as to bring valve piston, A, toward the opposite end; the exhaust steam from the steam chest escapes from before it, through the exhaust port, K, the opening of which into the chest is at such a distance from the head as will permit sufficient exhaust steam to remain to afford a cushion to the valve piston.
Fig. 253.
Fig. 254.
Fig. 255.
Fig. 256.