The dynamics of hydraulic fluids - significance, differences and measuring

摘要

In this paper the most important dynamical properties of hydraulic fluids and the significance of fluid dynamics on hydraulic systems control are introduced. The bulk modulus, density and sound velocity of five different types of commercial hydraulic fluids were measured at different temperatures and pressures up to over 600 bar. The measurements were based on defining the pressure wave propagation time at known length of rigid straight pipe. The conventional measuring system had to be modified due to aeration and reflection problems which were revealed at pressures over 300 bar. Finally the results are discussed and compared with each other. The results are also compared with recent, relatively easy-to-use mathematical models for possible correlation.