Bearing/Seal Characteristics of the Film between a Valve Plate and a Cylinder Block of Axial Piston Pumps (3rd Report: Effects of Fluid Types and Theoretical Discussions)

An experimental study was carried out to clarify the effects of fluid types on the bearing/seal characteristics of the fluid film between a valve plate and a cylinder block of axial piston machines. The fluids tested were a kerosene, a solution type and a emulsion type high water base fluids. Including the results with petroleum based hydraulic fluids already reported, it can be seen that: (1) For the low viscosity fluids, the reduction in the load carrying capacity is compensated for the increase in both the inclination of the wedge film and amplitude of the squeeze film. Then, on the average, the fluid film can be as thick as the petroleum based fluids. (2) The lost power due to the frictional torque is smaller for the low viscosity fluids, but that due to the leakage flow for the petroleum based fluids. Since the latter is the dominating cause for this test, the total lost power of the low viscosity fluids is smaller only under the relatively low pressure conditions. Moreover, it was shown that the theoretical film thickness, obtained by the calculation including the spring effect of the shaft, agreed approximately with the experimental film thickness.