The valve piston in this pump is provided with packing rings, E, E, which compensate for wear of these parts so that this valve is expected to do efficient service long after a slow valve. The supplemental valve, F, has a reciprocating rotary motion which is communicated to it by the rock arm, G, and pitman, H, connecting with the crosshead, I, secured to the piston rod. It will be observed that the piston rod, J, and the rod, K, of the water end are separated so that should either one give out through wear or accident it can be replaced without sacrificing both, as would be the case if they were solid in one piece. This supplemental valve, F, in general appearance very closely resembles the “Corliss” valve, and its action is somewhat similar, in controlling the action of the valve piston, which will be understood from the engraving without further description. These pumps all have removable water ends and can be rebored or otherwise manipulated without disturbing the steam end of pump. The cylinder can be separated from the foot by removing the bolt, M. The duplex pump is also shown in the accompanying engraving, where, A, A, represents the steam cylinders, secured to the foot, B, by bolts, as previously described. The usual slide valves have been replaced by piston valves, C, in this instance and are provided with removable seats, D, D. These piston valves have packing rings, E, E, also to compensate for wear and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 [Illustration: FIG. 300.] THE DUPLEX STEAM PUMP. [Illustration: 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; 1-1/8-inch water cylinder; 2-2/3-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.