Reciprocating pump is a positive displacement pump. Main moving parts are pistons or plungers, therefore, reciprocating pumps are also called piston pumps or plunger pumps.
When the piston moves from left(inner dead center) to right(outer dead center), the volume of the pump’s right chamber will be reduced, followed by the increased gas pressure of the gas in the right chamber and the space of the valve chest will connect with the chamber via valve. The discharge valve will pen as a result of the increased pressure and the gas in the chamber will be discharged into the discharging pipe through the discharge valve. On the contrary, the volume of the left chamber will increase and gas pressure in the left chamber and the space connected with the chamber will decrease. Therefore, the suction valve will be opened due to the higher pressure in the suction line. The liquid will go up along the suction line and into the left chamber as a result of the low pressure in the suction chamber and pipe line. When the piston moves in the opposite direction, the right suction valve will be opened and the left discharge valve will be open.
Pistons keep doing the reciprocating movement, gas in the suction line is delviered into the discharge line continuously. Finally the liquid is drawn into the cylinder and further delivered by the pump.
The volumetric ratio of the liquid theoretically delivered by the pump in each revolution of the pump shaft to the average working space of the cylinder is called working number. To incrased the capacity, double-acting piston that delviers liquid on both sides is frequently used. With this arrangement, while one side of the piston is discharging fluid, the opposite end of the cylinder is drawing liquid. This sequence is reversed at the end of the stroke. Consequently, there are two suction strokes and two discharge strokes during every complete reciprocating cycle of the piston. Ordinarily, reciprocating pumps have two double-acting pistons or three(triples), five(quintuple), seven(septuple), or nine(nonuple) single-acting plungers.
