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A novel method for evaluating the source flow ripple and source impedance of positive displacement hydraulic pumps is described. The method is based on the measurement and frequency domain analysis of pressure standing waves in a pipe, and uses a secondary source of pressure ripple for excitation of the pump under test. The method is convenient, accurate and versatile and forms the basis of a new British Standard for measurement of a pump fluid-borne noise rating. Representative results are presented for an oil hydraulic pump and for a plunger pump for water-based fluid.

The noise levels generated by a variable capacity axial piston pump and a fixed capacity axial piston motor have been measured using Sound Intensity techniques; no special acoustic test environment was employed. The experimental procedures followed, as closely as possible, draft International Standard ISO/DIS 9614-4. Because the machines were mounted on existing test stands it was found difficult to comply completely with the requirements laid down in the draft Standard. Typical test results are presented showing that pump overall Sound Pressure levels increase significantly with increasing delivery pressure. The effect of discharge pipe length on pump noise levels is relatively small. From the motor noise tests, it was found that variations in speed were much more important than load. The work has highlighted the need for the development of Sound Intensity procedures specifically concerned with fluid power pumps and motors.