Single-Acting and Double-Acting Pumps:

A single-acting pump is one which takes suction, filling the pump cylinder on the stroke in just one direction, known as the suction stroke, and then forces the liquid out of the cylinder on the return stroke, known as the discharge stroke. A double-acting pump is one in which, as it fills one end of the liquid cylinder, is discharging liquid from the other end of the cylinder.

At the return stroke, the end of the cylinder only emptied is filled, and the end just filled is emptied. A single possible arrangement for single-acting and double-acting pumps is displays in Figure.