Abstract: The volume of the fluid leakage in the gaps of the hydraulic system is greatly influenced by the pressure, the temperature, and the air bubbles.The influences of these three factors on the dynamic viscosity, the heat expansion and the compression of the oil are investigated. A mathematical model of the fluid leakage is put forward also. The relations of the leakage ,the dynamic viscosity, and the volume modulus to the pressure, the temperature and the air bubble are obtained through numerical simulation, respectively. Moreover, the qualitative analysis on these three parameters is also given. The numerically simulated result that the peak value of the leakage varies with the pressure is quite useful for engineering purpose.

Key words: Gaps, Hydraulic system, Inner leakage, Peak-value change, Viscosity-pressure, Viscosity-temperature