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What are Reciprocating Pumps?

Paul Scott
Paul Scott

A reciprocating pump is a device designed to pump gases or fluids by means of pistons or a diaphragm. The term "reciprocating" describes any continuously repeated backward and forwards motion. Reciprocating pumps are positive displacement devices, i.e., they transport matter by displacing it with a moving object. Piston or plunger reciprocating pumps achieve this pumping action by alternately drawing fluid or gas into a piston cylinder through an inlet port then expelling it again via a discharge port. Diaphragm pumps, the other variant, work in a similar fashion and utilize the flexing of a diaphragm to displace the matter.

Any continuously repeated back and forward motion is known as reciprocating or reciprocal movement. In a reciprocating pump, this term refers to the cyclic action of a piston or a flexible diaphragm. In both cases, these components are used to move or transport fluids and gases by means of positive displacement. This describes a process of progressively displacing or moving matter in a closed space by introducing a moving obstruction such as a diaphragm or piston.

A pumpjack at the top of a reciprocating piston pump.
A pumpjack at the top of a reciprocating piston pump.

A piston pump consists of a piston and cylinder arrangement similar to an internal combustion engine. Each cylinder is equipped with an intake and outlet valve which operate alternately and are synchronized with the piston stroke. The initial down stroke of the cycle sees the piston drawing fluid or gas into the cylinder through the intake valve. At the bottom of the stroke, the intake valve closes as the piston comes up again and compresses the matter in the cylinder. Near the top of the stroke the outlet valve opens and allows the compressed material to be forced out of the cylinder.

As this process is repeated, a constant stream of fluid or gas is ejected from the pump via the outlet port. The compression ratio, rotational speed, number of cylinders, and cylinder capacity of the pump dictate its output capacity. Common uses of the plunger or piston reciprocating pump include well hand pumps, windmill pumps, and air compressors. Of the two types of reciprocating pump, the piston pump can deliver the highest pressure and flow rate. Piston reciprocating pumps are not suitable for pumping explosive or toxic mediums though.

Diaphragm type reciprocating pumps function on the same principle as a piston pump except that a flexible diaphragm supplies the displacement component. In this sort of pump, a diaphragm is alternately flexed up and down by a cam inside a sealed, valve equipped chamber. As the diaphragm starts the down cycle, an inlet valve opens and the vacuum caused draws fluid into the chamber. As the diaphragm moves up, both valves close for the compressive stroke, and then the outlet valve opens to allow the fluid or gas to escape. Diaphragm reciprocating pumps are often used on smaller compressors and can be suitable for pumping toxic or explosive materials.

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    • A pumpjack at the top of a reciprocating piston pump.
      By: Edelweiss
      A pumpjack at the top of a reciprocating piston pump.