What is Radial Piston Pump

What is a Radial Piston Pump?

A radial piston pump is a type of positive displacement hydraulic pump where the pistons are arranged radially (perpendicular) around a central drive shaft, inside a circular cylinder block. Their unique design makes them exceptionally robust and capable of generating the highest operating pressures of any common hydraulic pump type.

They are renowned for their durability, high-pressure capability, and long service life, especially in demanding, continuous-duty applications.

How Does a Radial Piston Pump Work?

The core principle involves the conversion of the rotary motion of the shaft into the reciprocating motion of the pistons. There are two main design variations:

1. Shaft-Driven / Eccentric Cam Type (Most Common)

This is the classic design. Here’s how it works:

1. Stationary Cylinder Block: The pistons are housed in bores within a stationary cylinder block.

2. Eccentric Drive Shaft: The rotating drive shaft has an eccentric cam (or an eccentric ring) around its centerline. This means the shaft is offset, creating a "lobed" effect.

3. Piston Movement: As the shaft rotates, the eccentric cam pushes the pistons inward toward the center of the pump in a specific sequence.

4. Spring or Pressure Return: The pistons are pushed back outward on the return stroke by either:

   • Springs: Located behind each piston.

   • Centrifugal Force: The rotation itself flings the pistons outward.

   • Low-Pressure Oil: From a small charge pump.

5. Valving - The Stationary Pintle: A critical component is a fixed pintle (a central valve) inside the pump. This pintle has two channels:

   • Inlet Port: As a piston moves outward (on the suction stroke), it passes the inlet port of the pintle, drawing fluid into the cylinder bore.

   • Outlet Port: As the cam pushes the piston inward (on the pressure stroke), it passes the outlet port of the pintle, forcing pressurized fluid into the system.

2. Rotating Cylinder Block Type (Less Common)

In this design, the cylinder block rotates with the shaft. The pistons are connected to a stationary reaction ring. The eccentricity between the rotating block and the stationary ring causes the pistons to reciprocate. The valving is typically achieved through port plates.