What is a Simplex Pump?

Simplex (Pump): A simplex is the designation of a reciprocating pump which utilizes a single drive rod design.


Simplex pumps use a single drive rod to pump the fluid. They are available in both single and dual acting designs.

The number of pump chambers is not the best way to determine if a pump is a simplex design. The pump may have a single pumping chamber in a single acting pump, and two chambers in a dual-acting pump. However, both are considered a simplex pump because they only use a single drive rod.

Simplex Pump Properties

Simplex pumps are a simpler design than other reciprocating pumps that use more drive rods (such as triplex, or quintuplex). This simple design makes it easier to use, repair, and maintain. Their cost also tends to be lower due to a lower number of moving parts. Despite these benefits, simplex pumps have flow variations that require additional consideration when designing a pump system.

The image below references a single action simplex piston pump. Notice that fluid is only moving through the inlet of the pump when the piston is drawing back. Similarly, fluid is only moving through the outlet when the piston is pushing into the pumping chamber. As a result, the pump is only providing flow 50% of the time. The fluid in either the inlet or outlet is stagnant for 50% of the time.

This change in flow creates pressure pulsations and acceleration head. Each time the flow changes from stagnant to flowing, or flowing to stagnant, pressure differentials are created through the pump and the surrounding piping. Depending on the amplitude of these pulsations, damage to the pump and surrounding system may be possible.

These pulsations can be relieved by providing a vent to atmospheric pressure, or through a pulsation dampener. It is important to ensure the correct design of the system to prevent potential problems created by the changing flow.

The uneven flow characteristics for simplex reciprocating pumps can be seen below. Notice that the velocity of the flow reaches up to 320% of the average flow velocity for a single action, and up to 160.2% for a dual-action. For example, if pumping fluid at a flow rate of 10 GPM in a single action simplex pump, the flow is fluctuating between 0 and 32 GPM with each rotation of the crankshaft.

Dual Action Simplex Pump Flow Characteristics

Example Uses for Simplex Pumps

Despite uneven flow characteristics, simplex pumps can be good candidates for:

  • Pump Jacks
  • Steam Pump
  • Water Jetting
  • Water Wells
  • Metering Pump
  • Glycol Circulation
  • Injection Molding
  • Hot Oil
  • Hand Pumps

Contact us today to have us help you set up your pumping systems!

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