Bulk modulus measurement of hydraulic oil based on drop-hammer calibration device

Hydraulic oil bulk modulus is acquiescently set as constants in practical engineering application, so that the theoretical predicted pressure from drop-hammer calibration device will be much different from the measured one. In this situation, bulk modulus measurement of hydraulic oil in the basis of the drop-hammer calibration device is proposed. The practical model for bulk modulus of hydraulic oil was established according to the analysis of the cause to the data errors. With the help from the existing drop-hammer calibration device, "pressure piston displacement" data pairs were got to work out the model parameters further, and the bulk modulus change rule was obtained. The comparison experiment between the theoretical predicted pressure using the new model and the measured value shows that the bulk modulus model being built is simple and practical. It indicates that the prediction accuracy is less than 2.0% when the pressure is within hydraulic oil\´s compression prosperities (under 500MPa); the accuracy is less than 3.5% in the pressure extrapolation area (500MPa or more). It meets the requirements of engineering application.