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Every hydraulic system use requires a pump to supply the necessary flow and support the imposed pressure cycle. Therefore the performance of the pump in a hydraulic system is critical to the overall performance of the system. It is a well known fact that the performance of a hydraulic pump is influenced by both the speed at which it is operating and the pressure to which it is subjected. This paper evaluates the volumetric efficiency of a hydraulic pump using both the fundamental expressions which are generally accepted and actual data test data. The widely accepted equation for pump leakage is presented along with an expression that includes the parameter of speed. Results obtained using a pressure-loaded gear pump are used to compare and evaluate the analytical expressions. This comparison reveals a significant influence of speed at high pressures on the volumetric efficiency of the pump.

The multipass filtration performance test which has recently gained industry-wide support offers many fundamental ways of describing the performance characteristics of fluid power filter elements. Some of these descriptions are uniquely qualified to provide the system designer with a practical technique for appraising the capability of filter elements. Important appraisal parameters of a filter element which must be considered by a designer are particle separation capability, contaminant capacity, and pressure loss. In order to specify a filter element properly for a given application, the requirements for the appraisal parameters must reflect the needs of the system components. A practical and fundamental description for the performance of fluid power filters will incorporate appraisal parameters which can be related to the demands of such system components.