Further Test Results of the Leading-Edge-Groove (LEG) Tilting Pad Thrust Bearing

A. M. Mikula, Director of Marketing
Kingsbury, Inc., Philadelphia, PA 19154


This paper compares the LEG and pressurized controlled flow lubricant supply methods and evaluates their influence on the babbitt temperature and bearing power loss performance of a tilting pad, equalizing thrust bearing. The paper also presents new experimental temperature data from bidirectional testing of a unidirectional LEG bearing. The experimental data presented is from a 267 mm (/0.5 ill.) O.D. bearing, operating at shaft speeds up to 13000 rpm with applied loads that produced mean unit pressures of up to 3.45 MPa (500 psi). Conclusions are drawn based upon these test data.


The leading-edge-groove (LEG) tilting pad thrust bearing is a low frictional loss hydrodynamic thrust bearing that utilizes a managed oil flow lubrication concept. The bearing is so named because the leading edge of each pad or shoe is extended to accommodate an oil distribution groove. Cool, undiluted lubricant is introduced from this groove directly into the fluid film of each shoe. This method of supplying oil into the hydrodynamic wedge has been found to significantly reduce bearing frictional power losses and babbitt temperatures [1, 2).

In this third paper of leading edge groove thrust bearing test results, the oil supply method was isolated and evaluated to determine its influence on bearing performance. The two previous papers [1, 2] compared offset pivot (60 percent) LEG and central pivot (50 percent) conventional thrust bearings. Elwell and Leopard in reference [1), and Martin and Gardner in reference [2] questioned whether the LEG temperature advantage was a result of the lubrication supply method or pivot location. This paper presents test data that addresses that question. The two primary indicators of bearing performance-frictional power loss and babbitt temperature-are used to contrast leading edge groove and pressurized supply (controlled flow) bearing results. Each bearing was tested under identical conditions of applied load, oil supply flow rate, shaft speed, oil supply temperature, pivot offset, and oil viscosity. Details of the bearing test rig can be found in reference [3].

Bidirectional operation test data for the LEG bearing is also presented. Babbitt temperature comparisons are made to contrast proper and reverse shaft rotation. Each bearing shaft rotation direction was tested under identical conditions of applied load, shaft speed, oil supply temperature and oil viscosity. Temperature differences can be attributed to shaft rotation direction and, therefore, pivot and oil supply gro( location.

The bearings were evaluated using a light turbine (ISO I. 32) oil with a viscosity of 0.027 Pa·s @ 37 .8°C and 0.00'?i. @ 98.9°C (150 SSU @ 100°F and 43 SSU @ 210°F) supplied at 46°C (115°F), for applied loads that produced mean unit pressures ranging from 0- 3.45 MPa (0- 500 PSI) and shaft speeds ranging from 4000-13000 rpm. The oil supplied to each bearing was controlled by a throttling valve and measured with a turbine flowmeter.

The performance data presented isolates and identifies the individual contributions of shoe pivot location and oil supply method. These issues were raised in the discussion of the two previous papers [1,2], and based on this test data, should now be resolved.

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