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How To Design And Install Plumbing

There are three types of piston pumps:
1. Single-action pump
2. Double-action pump
3. Duplex or twin piston pump
Single-action Pump. The working principle of a single-action pump is very simple. It consists of a cylinder constructed of cast iron, into which a piston is fitted accurately. The piston is made of cast iron or bronze and is equipped in most installations with leather cup packings, Fig. 207.

The suction side of the pump is equipped with a valve, A, which opens when the piston is drawn in the cylinder. Moving the piston in the cylinder removes atmospheric pressure and creates a partial vacuum. The atmospheric pressure on the surface of the water forces the water into the suction pipe, Fig. 208. The valve opens and the cylinder is filled with water.

The delivery side of the pump is also equipped with a valve, B.

After the suction or draw stroke of the piston has been completed and the cylinder is full of water, the return 'or power stroke drives the piston against the confined water. The suction valve closes and the confined water forces open the valve on the delivery side of the pump, allowing the water to pass through it, Fig. 209. AVhen all the water has been expelled from the cylinder the suction stroke begins, again filling the cylinder.

Double-action Piston Pump. The double-action type of pump is similar to the single-action type in its operating principle. The difference is that the double-action pump contains four valves instead of two and delivers water on both the suction and delivery stroke of the piston, Fig. 210.

When the piston of a double-acting pump is put in motion, the valve on the suction sifle of the piston is opened. At the same time, the valve on the delivery side of the piston opens, thus allowing the confined water to be discharged from the cylinder, Fig. 211. Reversing the piston movement, the suction valve on the opposite side of the piston opens and allows water to re-enter the discharge side of the cylinder. Water confined on the opposite side of the piston is forced from the cylinder by the piston action, Fig. 212. Simultaneous opening and closing of the pump valves is effected by the action of springs, gears, or cam mechanisms.