Principle of Operation:

All positive displacement pumps operate on the similar basic principle. This principle could be most simply elaborates through considering a reciprocating positive displacement pump consisting of a single reciprocating piston within a cylinder along with a single suction port and a single discharge port as displays in Figure. Check valves in the suction and discharge ports permits flow in only one direction.

Figure: Reciprocating Positive Displacement Pump Operation

In During the suction stroke, the piston moves to the left, causing the check valve within the suction line between the reservoir and the pump cylinder to open and admit water from the reservoir.

In During the discharge stroke, the piston moves to the right, seating the check valve in the suction line and opening the check valve in the discharge line. A volume of liquid moved through the pump in one cycle (a single suction stroke and a single discharge stroke) is equal to the modification in the liquid volume of the cylinder as the piston moves from its farthest left position to its farthest right position.