These piston valves have packing rings, E, E, also to compensate for wear and the valves are cast hollow to reduce their weight as much as possible consistent with good workmanship, also to serve as ports for steam admission. When these valve seats become worn they may be easily removed and rebored or replaced by new ones, as desired. It will be observed that these ports are very short to reduce the clearance as much as possible, and to secure a more satisfactory cushion. Each valve is operated by the rock arm connected with the opposite engine in the usual way.
THE DUPLEX
PUMP
Fig. 300.
THE DUPLEX STEAM PUMP.
Fig. 301.
The word duplex means two fold, or double, and has a wide application, as the duplex lathe, the duplex watch, etc., hence, the well-known duplex-pump is one in which two direct acting pumps are placed side by side and so connected that the steam piston of one operates the valve of the other. See [Fig. 300].
[Fig. 301] shows one of the smallest manufactured patterns of this type of pumps. Its dimensions are as follows: 2-inch diam. steam cylinder; 11⁄8-inch water cylinder; 22⁄3-inch stroke. Its capacity is .044 gallons per revolution; rev. per minute, 80; gallons per minute, 3.5. Steam pipe, 3⁄8-inch; exhaust pipe, 1⁄2-inch; suction pipe, 1-inch; discharge, 3⁄4-inch. Floor space occupied, 1´ 9″ × 7″ wide; requires 1⁄2 H.P.