What is a Simplex Pump?

Paul Scott

A simplex pump is a single piston reciprocating device that displaces fluids on both stroke cycles. In other words, the cylinder is filled with fluid above and below the piston, and pumps on both the up and down stroke. Simplex pumps may be powered by electric, gasoline, or diesel motors or by compressed air. They are also frequently used in hand operated hydraulic pumps. The simplex pump is a particularly efficient design capable of producing excellent delivery rates with minimal input energy.

Firefighting water supplies are also often delivered by simplex pumps.
Firefighting water supplies are also often delivered by simplex pumps.

Unlike conventional reciprocating pumps which only displace fluid on one stroke of their cycle, the simplex pump moves fluid on both the up and down stokes through ports on either end of the cylinder. As the piston moves up the cylinder, it draws fluid through the lower port, forces fluid out of the opposite port, and reverses the cycle on the next stroke. This dual directional pumping action is made possible by a valve equipped, multi-chambered manifold that connects to the two flow ports. The manifold typically contains a pair of chambers for each flow port and each side of the piston. Each chamber is fitted with a valve that controls the flow of fluid through it.

As the simplex pump cycles, each side of the piston alternately draws fluid into one of its chambers and out of the other. The valves and chambers are arranged in such a way that the output chambers for each side of the piston vent into a common outlet. This pumping arrangement means that there is no “dead” spot or stroke in the cycle. This characteristic makes the simplex pump a particularly efficient design and capable of delivering excellent output values with low input energy requirements.

Simplex pumps are available in many different sizes ranging from large capacity water pumps to smaller varieties used to pressurize hydraulic tools. The double cycle action and low power requirements of the simplex pump make it ideal for hand operation as it requires little cycling to attain adequate pressure and needs no complex linkages or gearing to operate. Larger simplex pumps are typically driven by electric motors of gasoline and diesel engines. Compressed air is also occasionally used to drive some pumps.

Simplex pumps are found in a variety of applications which require low power, high delivery performance. Large ships utilize simplex pump banks to supply fuel oil to their engines as do fuel oil fired furnaces. They are also commonly used as bilge pumps on larger vessels. Firefighting water supplies are also often delivered by simplex pumps.

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