Measurement and Prediction of the Fluid-Borne Noise Characteristics of Hydraulic Components and Systems

D N Johnston

PhD Thesis

University of Bath



The flow ripple from positive displacement pumps is one of the main sources of fluidborne noise in hydraulic systems. A new experimental method for the measurement of the source flow ripple and source impedance characteristics of positive displacement pumps, called the 'Secondary Source' method, has been developed. Extensive testing on a variety of pumps proved that the method is effective and that it has several advantages over previous methods, being quick. accurate and versatile. Experimental flow ripple and source impedance results are compared with theoretical models. Correlation with and deviations from the models are investigated.

The Secondary Source method was also applied to the measurement of the impedance characteristics of valves and an accumulator. The accumulator impedance results show very good correlation with a simple theoretical model. Discrepancies are observed between valve impedance measurements and a simple resistance model. Several causes of these discrepancies are isolated, including fluid compressibilitv and inertia, and valve vibration.

A method for the accurate measurement of the speed of sound in the fluid in a pipe is described. This was applied as an integral part of the Secondary Source method, and is shown to give good results.

Using information obtained from the Secondary Source method, a computer-based simulation package was developed for the prediction of the pressure ripple characteristics of complete hydraulic circuits. This package is useful for the study of the resonant characteristics of circuits, in order that low pressure ripple circuits can be designed. The effectiveness of several different methods for the reduction of fluid-borne noise is discussed.

An electronic version of this thesis is available on request.

Centre for Power Transmission and Motion Control

Department of Mechanical Engineering