In Fig. 207 is shown a double acting power pump used principally for feeding boilers but may be employed for any purpose in forcing water or other liquids against pressure. This pump is double acting, is made with four _check valves_, as shown in engraving, and will draw water through 25 feet of suction pipe. On a high lift like the foregoing a foot valve (as shown at D in Fig. 204) should be used. [Illustration: FIG. 207.] The form of valves used in this type of pump are the regular commercial check valves, made of steam-metal, extra heavy; the valve proper is of the _wing_ pattern as shown in the small cuts. There are four of these wings on each valve, at right angles to one another forming a cross with arms of equal lengths. [Illustration: STRAIGHT WINGS.] [Illustration: SPIRAL WINGS.] The seat of the valve has an angle of 45° to which the valve is adjusted. A part of this valve projects above the top and has a slot, shown by the dotted line in it to receive the edge of a screw-driver, held in a bit stock to grind the valve seat in refitting. The lift of the valve is regulated by the distance between the top of the stem and the bottom of the covering nut or cap. In hydraulic pumps it is found to be good practice to give the wings of these valves a twist, or pitch, so that the water in passing through will cause the valve to rotate and fall in a new position every time it comes in contact with the seat. Fig. 208 represents a very compact design of _double acting low service belt driven pump_. The water cylinder is bored and has a piston fitted to it; both ends of this cylinder are covered with “heads,” one of which has a stuffing box through which the piston operates; the outer end of this piston rod is fitted to a slotted yoke which slides upon a guide at the bottom. This mechanism, just described, takes the place of a pitman connection and occupies very much less space. The crank shaft is supported at each end in pillow blocks and is driven by a belt having a tight and loose pulley; larger sizes are geared. Access to the two sets of valves can be had by slacking up four nuts upon the long belts, two of which are shown in the engraving. The broad base secures great stability for this size pump. [Illustration: FIG. 208.] [Illustration: FIG. 209.] [Illustration: FIG. 210.]