The impedance characteristics of fluid power components: relief valves and accumulators

This paper describes an experimental and theoretical investigation of the impedance characteristics of various relief valves and an accumulator. The test programme involved the measurement of pressure ripples at three locations in a specially designed test circuit. From these measurements, the impedance of a component was evaluated as a function offrequency. The experimental results are compared with mathematical models. For a single-stage relief valve, a simple orifice model has been found to be adequate. For two-stage valves, a much more complex model was considered. This was found to predict the basic trends but was not accurate. Tests on an accumulator yielded results which correlated well with a relatively simple mathematical model. However, it is difjicult to quantify the model parameters. It is concluded that for the more complex components used in hydraulic systems it is necessary to measure the impedance characteristics rather than predict them. There is a need to adopt a standard test procedure for this purpose.