The New Generation Radial Piston Pump Offers Many Advantages to Injection Molding Applications

Moog has recently introduced a new generation of the proven Radial Piston Pump called RKP-II that has a significant reduction in noise and a longer lifespan. This new version has important design changes and improvements such as completely reengineered housing with an increased number of pistons and a sliding stroke ring. RKP-II models can be equipped with a proportional valve with digital on-board control electronics for volume flow and pressure control.

RKP-II Meets the Requirements of the Plastics Industry

Well-known in the industrial market for its reliability, suitability with special fluids, and low noise emission, the RKP has been an ideal solution for demanding applications such as plastics and die casting machinery for many years. The new design of RKP-II pumps in the sizes 63, 80 and 100 cc per revolution offers even greater durability and quieter performance.

With an electro-hydraulic digital p/Q control system, the pump is well suited for a variety of pressure and volumetric flow control applications. Hence it was adopted early on as a flexible solution in applications with sequential motion such as injection molding machines. It can achieve more dynamic and more precise control as well as a higher repeatability of machine operations. The ability to make “on-the-fly” changes of parameter sets makes performance optimization possible during the sequential machine processes with different actuators. The RKP-II, combined with an electro-hydraulic digital p/Q control, gives injection molding machine builders a competitive advantage through longer service life, lower noise emission, improved control options, expanded functionality, and easy commissioning.

New Stroke Ring Increases Stability and Lifetime

The RKP-II incorporates a flattened, sliding ring instead of a round stroke ring. The outer face of the new ring has a nearly rectangular surface, which supports the ring in the housing. This reduces the wear and tear on the entire actuator system. Machine stability and lifecycle are thus increased, even under demanding operating conditions.

Reduced noise levels

Moog has implemented important design changes to reduce the primary and secondary noise levels produced by the RKP-II. The number of pistons was increased from 7 to 9 for sizes 63 and 80 cc per revolution, enabling a reduction in piston diameter. This has reduced the dynamic alternating forces affecting the housing and noticeably decreased the circulatory and pressure pulsation on the high-pressure side.

Dead volume in the pistons has been reduced to a minimum due to the cup design of the working pistons. The pulsation amplitude of the RKP-II is thus significantly lower than the values exhibited by comparable piston pumps with external pre-compression volume. This is a contributing factor towards reducing the noise emitted by the system or machine. Noise emissions are further improved by the optimized flow design of the suction path. Pressure pulsation on the intake side is significantly less due to reduced hydraulic inductance.

Compliance with the European Union’s Noise Emission Guideline

The overall result of these design changes is that the noise pressure level of RKP-II models of size 63 and 80 cc per revolution does not generally exceed the 70-decibel mark even in demanding operating conditions. Thus, the Moog RKP-II actively supports machine and equipment manufacturers in implementing the European Unions noise emission guideline (2003/10/EG).

Optimized Suction Path

Another improvement in the standard design of the RKP-II is a larger intake connection (SAE 2" standard series, 3000 psi). The solution offers more robust suction behavior, optimum intake, and less pressure loss along the suction path. The optimized intake channel in the housing and control journal has reduced the incidence of cavitation in the housing, control journal and drive.

In addition to the wide range of hydro-mechanical control options (e.g., pressure compensator, combined pressure and flow compensator (load sensing controller), constant horse power control), the electro-hydraulic digital p/Q control is a new option for the RKP-II. The addition of a new proportional solenoid pilot valve with digital on-board electronics to the pump enables local loop closure, tuning and diagnostics. This digital p/Q control was the result of extensive research and development work, which led to performance and system optimizations never before possible with a servo pump. Among the other important improvements is the possibility to implement servo control in multi-pump arrangements in a master-slave version. With the master-slave solution, key parameters can be easily adjusted "on the fly", while real-time diagnostic data remains available via the man-machine interface (MMI) of the machine or via a laptop pc interface. This version of the RKP-II is one of the most advanced solutions in the marketplace today.


Dirk Becher has been Engineering Manager for radial piston pumps at Moog since October 2004. He has a doctorate in engineering sciences and was previously involved in the development of axial piston pumps at Eaton Fluid Power GmbH.