Radial Piston Pump

A radial piston pump is a robust positive displacement pump that generates high pressures of up to 1000 bar in hydraulic systems. Pistons move radially in a star pattern around the drive shaft, sucking in fluid and pushing it out with a volume flow. Engineers value them for their low-pulsation delivery in demanding B2B applications such as construction machinery.

Design of the radial piston pump

Radial piston pumps are based on a compact principle that enables high power density. The core consists of a cylinder block with radial bores in which several pistons – often more than five – are arranged in a star shape. An eccentrically running drive shaft drives the rotor and generates the piston stroke.

The pistons slide in the cylinders and are supported either internally or externally. In the version with internal piston support, the pressure acts via the drive shaft; with external support, the pump housing presses the pistons inwards. A suction chamber holds the hydraulic oil, and a valve plate controls the inlet and outlet. The thick-walled steel housing protects against high loads and integrates channels for the suction and pressure sides.

Manufacturers such as Bosch Rexroth and Moog adapt the design to specific requirements. A raceway moves eccentrically to regulate the displacement. Seals and bearings ensure durability at speeds of up to 3000 rpm.

• Pump housing: Supports all components and dissipates pressure.
• Rotor and piston: Perform the displacement process.
• Control element: Enables volume control.

This design significantly reduces axial forces on the shaft and also reduces wear.

How a radial piston pump works

The drive shaft rotates and moves the rotor eccentrically. Pistons push out radially, increasing the cylinder volume and creating negative pressure. Hydraulic oil flows in from the suction chamber. During the return stroke, the pistons push out the fluid and the pressure rises rapidly.

Each piston goes through the suction and pressure phases in a staggered manner, which provides a steady flow without strong pulsations. The flow direction is radial from the inside to the outside. Valves in the plate open and close automatically, depending on the differential pressure.

During regulation, a servomotor shifts the eccentric. The displacement volume decreases or increases, and the flow rate adjusts accordingly. Some models reverse the flow by adjusting beyond the zero position. This mechanism ensures precise control in closed circuits.

Engineers test the function on test benches, where pressure and torque are measured in real time. This allows technicians to ensure that the pump runs stably under load.

Advantages of radial piston pumps

Radial piston pumps impress with their strengths when it comes to demanding requirements. They achieve pressures of up to 1000 bar with high efficiency, even at low speeds from 500 rpm. Low pulsation protects downstream components such as valves and cylinders.

The compact design fits into tight machine rooms, and the radial arrangement eliminates axial shaft forces. This extends the service life. In addition, they continuously regulate the volume, which saves energy.

• High pressure build-up without loss of performance.
• Low pulsation, ideal for sensitive systems.
• Durable thanks to robust construction.

Technical buyers choose them for applications where reliability counts.

Disadvantages and challenges

The complex design drives up costs compared to gear pumps. Thick-walled housings and precise seals make manufacturing costly. Contaminants in the oil cause pistons to wear faster because tolerances are tight.

High torques require powerful drives, and the overall height sometimes exceeds that of axial piston pumps. Maintenance requires specialist knowledge, as disassembly is time-consuming.

Nevertheless, the advantages outweigh the disadvantages in high-end applications.

Typical applications in the B2B sector

Radial piston pumps are used where high pressure and precise flow are required. In construction machinery such as excavators or wheel loaders, they supply travel and steering systems. Presses in manufacturing use their stable pressure build-up for forming and punching.

Production managers use them in machine tools, such as injection molding machines. Mobile hydraulics benefit from their reversibility. Plant operators in the steel industry appreciate their durability under continuous load.

HK Hydraulik repairs such pumps on modern test benches and ensures full functionality.

Comparison with other hydraulic pumps

Radial piston pumps stand out due to their radial design and pressure strength. Here is an overview:

Axial piston pumps are flatter, but are suitable for lower pressures. Gear pumps score points for simplicity, but lose out in terms of pulsation.

Technical data and control options

Typical radial piston pumps deliver volume flows of 10 to 250 l/min at speeds of 500–3000 rpm. Pressure depends on the number of pistons and the stroke – Hawe models achieve 700 bar continuous pressure.

Control is mechanical-hydraulic or electrical. An actuator shifts the raceway, continuously adjusting the displacement volume. Pressure control automatically limits the outlet pressure.

Standards such as ISO 10771 define test procedures for positive displacement pumps. Manufacturers list data sheets with accuracies of 0. 1% for torque measurement.

Maintenance and repair of radial piston pumps

Service technicians regularly check radial piston pumps for leaks and wear. Frequent defects are caused by cavitation or dirt: pistons jam, seals fail.

Maintenance includes:

1. Oil changes according to manufacturer’s specifications.
2. Filter inspection and lubrication of bearings.
3. Vibration measurement for early detection.

During repairs, experts disassemble the housing, replace pistons, and test on test benches. Test benches simulate loads of up to 500 bar and 1000 l/min and record data digitally. This enables plant operators to minimize downtime.

Norms and standards for radial piston pumps

ISO 10771 regulates tests for piston pumps, DIN EN ISO 3019-1 specifies general requirements. VDE 0113 supplements electrical control. Manufacturers certify according to these standards to ensure interoperability.

Students learn these standards during their training in order to dimension systems safely.

Radial piston pumps dominate demanding hydraulic systems thanks to their power. Technicians and purchasers rely on them when pressure and precision count.