Radial piston pump ensures high pressures

A radial piston pump is a type of hydraulic delivery pump. It is characterized by its ability to reach very high pressures of up to 1,000 bar.

Design of a radial piston pump

In a radial piston pump, the pistons are arranged circularly around the drive axis. They thus act from the inside out along an eccentric circular path. Their main difference from the axial piston pump is that in this design, the pistons are arranged parallel to the drive axis.

The components of a radial piston pump:

• Pistons (usually more than 5)
• Shaft with cylinder bores
• Housing
• Intake port
• Pressure port

The pistons are embedded in the cylinder bores of the shaft. To enable continuous circular motion, the shaft is centered in the housing, but the pumping area is slightly offset, resulting in an eccentric movement.

Operating principle of radial piston pumps

A distinction is made between two designs of radial piston pumps:

• Internally supplied, externally supported pump
• Externally supplied, internally supported pump

In the internally supplied pump, the pistons suck in the hydraulic fluid through the drive shaft, which is designed as a hollow shaft, and are supported by the housing wall.

In the externally supplied pump, the pistons suck in the hydraulic fluid from the outside and are supported by the inner shaft.

Each working piston rests against its support at the inner dead center. After half a revolution, the piston has completed its suction stroke and has completely filled the working chamber in the cylinder with hydraulic fluid. As the shaft continues to move, the piston returns to its dead center, pushing the previously sucked-in hydraulic fluid back out through the pump’s pressure port.

Advantages of radial piston pumps

Radial piston pumps are characterized by the following advantages:

• Very high efficiency – low heat generation
• High operating pressure of up to approx. 1,000 bar achievable
• Low pulsation effects, resulting in less risk of cavitation
• High load achievable even at low speeds
• Engine forces act only radially, not axially – gentle on bearings and shafts
• Very durable

Disadvantages of radial piston pumps

A disadvantage of radial piston pumps is their relatively complex design compared to screw or vane pumps. The achievable operating pressures require a very rigid construction with thick-walled housings and generously dimensioned seals. The radial piston pump has a fairly wide footprint. This makes it a somewhat bulky component in a hydraulic system. However, it is quite short, so its wide installation can be compensated for by clever planning of the hydraulic system.

Use of radial piston pumps

Radial piston pumps are used where high operating pressures are required. This applies, for example, to the entire construction and industrial vehicle industry. Here, it is listed as a standard component alongside the axial piston pump.

Other areas of application for the radial piston pump include:

• Hydraulic presses
• Clamping hydraulics on injection molding and die-casting machines
• Machine tools: Hydraulic clamping of tools or workpieces
• Vehicle construction: Power steering pumps and level control pumps for suspensions

Defects in radial piston pumps

Despite their complex design, radial piston pumps are generally very durable. As long as the hydraulic fluid is changed regularly and permanently filtered reliably, there is hardly any internal wear on the piston drive. However, the hydraulic oil should also always be within the specified temperature ranges. This may make the additional installation of an oil cooler necessary for the operation of a radial piston pump. Otherwise, the biggest weak points of a radial piston pump are the seals on the shaft and housing. However, these are usually easily replaceable.