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.
Straight Wings.
Spiral Wings.
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.
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.