Static Load Performance of a Water-Lubricated Hydrostatic Thrust Bearing

Abstract

In rotating equipment, thrust bearings aid to balance axial loads and control shaft position. In turbomachinery, axial loads depend on shaft speed and pressure rise/drop on the impellers. This paper details a water-lubricated test rig for measurement of the performance of hydrostatic thrust bearings (HTBs). The rig contains two water-lubricated HTBs (105 mm outer diameter (OD)), one is the test bearing and the other a slave bearing. Both bearings face the outer side of thrust collars of a rotor. The paper shows measurements of HTB axial clearance, flow rate, and recess pressure for operation with increasing static load (max. 1.4 bar) and supply pressure (max. 4.14 bar) at a rotor speed of 3 krpm (12 m/s OD speed). Severe angular misalignment, static and dynamic, of the bearing surface against its collar persisted and affected all measurements. The HTB axial clearance increases as the supply pressure increases and decreases quickly as the applied load increases. The reduction in clearance increases the flow resistance across the film lands, thus reducing the through flow rate with an increase in recess pressure. In addition, an estimated bearing axial stiffness increases as the operating clearance decreases and as the supply pressure increases. Predictions from a bulk flow model qualitatively agree with the measurements. Alas they are not accurate enough. The differences likely stem from the inordinate tilts (static and dynamic) as well as the flow condition. The test HTB operates in a flow regime that spans from laminar to incipient turbulent. Quantification of misalignment at all operating conditions is presently a routine practice during operation of the test rig.