At the maximum supply pressure of 62 MPa tribological characteristics of dynamically loaded hydrostatic thrust bearings were examined experimentally in mixed to fluid film lubrication. The outer radius of the bearings tested was 10mm and the ratio of the recess radius was 0.5. The bearings were made of carbon steel, bearing steel and polyetheretherketone (PEEK) with the surface roughness of 0.3 to 2.3 μmRa. The loads were fluctuated sinusoidally up to 5Hz by the electro-hydraulic circuit consisted of a hydraulic cylinder with a servo valve and a PC controller. The frictional torque and leakage flow rates were measured; the power losses were evaluated. In conclusion, i) As the frequency and amplitude of fluctuation of the loads increased, the hydrostatic balance ratio, where the frictional coefficient and the power loss increased, became small; ii) When the supply pressure and the loads were lower, the effect of the fluctuation was notable; iii) The fluctuation less influenced the leakage flow rate, and iv) Under marked elastic deformation conditions, the effect of the fluctuation was insignificant.

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