A review of recent and current research on the control of fluid power systems is presented. Strengths and weaknesses of different schemes for control at both the component and system level are identified. It is argued that the selection and tuning of the controller is a critical part of system design and that simulation has an essential role to play in this process.

Tests have been performed on a range of different poppet and disc valves operating under steady flow, non-cavitating conditions, for Reynolds numbers greater than 2500. The working fluid was water, and the axisymmetric valve housing was constructed from clear perspex to facilitate flow visualization. Measured flow coefficients and force characteristics show marked differences depending on valve geometry and opening. These differences are explained with reference to visualized flow patterns.

The difficulties involved in measuring a pump fluid-borne noise rating are discussed. A new test method is described for measuring the source flow ripple and source impedance of positive displacement hydraulic pumps. This is called the ‘secondary source’ method, and is based on the analysis of the wave propagation characteristics in a circuit which includes the pump under test and an additional source of fluid-borne noise.

The suction dynamics of axial piston pumps become more critical if the pump is to be used at high speeds. In order to prevent air-release and cavitation from occurring within the pump it is necessary to pressurise the pump inlet. As the speed of a pump is increased, higher boost pressures are required, due to the extra losses incurred through the suction line and portplate at the higher flowrates. However, the lack of data regarding axial piston pump behavior at high speeds creates problems for the system designer in selecting suitable boost conditions and for the pump designer in selecting the portplate configuration that is required to reduce fluid-borne-noise levels. This paper discusses the suction performance of piston pumps, and presents experimental and simulation results exploring the behavior of a high-speed axial-piston pump. Different air-release and cavitation models that are suitable for simulation studies are investigated.

The reduction in source flow ripple in hydraulic systems is the most effective method of reducing pump-generated pressure ripple and system noise. This paper describes reductions in axial-piston pump delivery flow ripple achieved using a novel timing mechanism which is inherently speed, flow and pressure sensing. Fixed-speed tests have shown that the mechanism can significantly reduce axial-piston pump delivery flow ripple over a wide range of delivery pressures and pump displacements. Furthermore, the reduction in pressure ripple achieved with the mechanism has been shown to contribute towards reductions in overall air-borne noise levels of up to 6 dB in a simple system. A simulation model has been produced to predict the behaviour of the prototype mechanism. The model has been compared with the measured delivery flow ripple and achieves good agreement.