Identification of Fluid Power Component Behaviour Using Dynamic Flowrate Measurement

An identification concept is developed utilizing direct measurement of the transient flowrate and pressure to determine the dynamic characteristics of fluid power components. The fundamental experimental approach is discussed and applied to a range of sizes of a bladder-type accumulator and also to a single-stage pressure relief valve. The gas charging characteristic of the accumulator was determined for three different sizes and during dynamic operation. It is shown how the nitrogen gas index of compression varies during operation and a relationship between the index and instantaneous flowrate is proposed. Measurements obtained with the pressure relief valve were used to identify its dynamic impedance in the frequency domain via time series analysis and transformation. The predictions are compared with a linearized mathematical model showing good correlation over a wide frequency band. A particular feature was found to be the use of the impedance magnitude-frequency asymptotes for validation of the steady state pressure-flowrate characteristic.