Effects of Tilt on the Performance of Hydrostatic Thrust Pads

Abstract

The majority of hydrostatic thrust bearings are designed on the assumption that the bearing surfaces are parallel but, with the possibility of manufacturing and assembly errors and structural deformations, this condition is rarely, if ever, achieved in practice. With the increasing demands being made in modern machinery, more detailed design information is required. An experimental and theoretical investigation was carried out into the effects of tilt on the operation of circular hydrostatic thrust pads, the results of which show that, for static conditions, the characteristics of a tilted pad can be reliably predicted, assuming the lubricant to be isoviscous. With this information, a thrust pad can be designed to operate in any specified tilted configuration or can be incorporated in a rigorous structural design. In many applications, however, it may be difficult to specify the tilt and in such situations it is more useful for the designer to have some indication of how the operating conditions may be modified by tilt when the design is based on parallel surfaces. For a system which is supplied from a constant pressure source through a viscous external restrictor, the modified operating conditions can be predicted. The effect of tilt on the operating conditions depends on the pad geometry and design resistance ratio but significant changes may occur in mean pad clearance, required flow rate and static stiffness. Although this investigation was limited to static conditions, the results are still valid for sliding conditions where the hydrodynamic effects are small compared with the hydrostatic contribution. The general effects of tilt observed with circular pads are indicative of what may be expected with pads of other geometries.