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What is a Radial Piston Pump?

Kirsten C. Tynan
Kirsten C. Tynan

A radial piston pump uses a drive shaft to drive pistons into and out of cylinders arranged perpendicular to the shaft in order to pump fluid. The motion of the pistons back and forth pumps fluid through the pump. A radial piston pump differs from an axial piston pump in the way that the pistons and cylinders are arranged parallel to the drive shaft.

In this type of pump, multiple pistons and cylinders are housed in a cylinder block evenly spaced around the drive shaft. There is typically a bearing ring, off-center with respect to the drive shaft, which causes the reciprocating motion of these pistons. Springs keep the pistons in contact with this ring as they move back and forth. The position of the ring determines the distance the piston travels and thereby determines the amount of fluid that can be drawn and expelled in one cycle. More fluid can be pumped the more off-center this ring is positioned.

The pumping cycle takes place in two phases. On the upstroke of the piston, fluid is drawn into the cylinder. As the ring moves and the piston’s position changes, the fluid is expelled out of the cylinder.


The two basic types of pistons used in these pumps are those shaped either as cylinders or as balls. Valves in each cylinder control the intake and outlet of the fluid being pumped. Other design variations include options for remote maintenance by computers and on-board electronics for controlling volume and pressure.

A radial piston pump may be a fixed displacement or a variable displacement design. In a fixed displacement pump, a set amount of fluid is pumped in each cycle and cannot be changed. The amount of fluid pumped in a variable displacement design is adjustable. This may be accomplished in radial piston pump designs by changing the position of the ring, by shutting down one or more of the pistons, or by another method.

Given its reliability, low noise, and suitability in high-pressure situations, many operations make use of a radial piston pump. Manufacturing applications include use of radial piston pumps in heavy machinery such as metalworking tools as well as test and simulation equipment. They may be used in power generation and transmission operations, both onshore and at sea. Their high performance at relatively low speeds makes them good choices for use in cranes and agricultural equipment as well.

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