Bearing - Other Practical Notes

Alarm and trip set points are important for efficient and reliable operation. These set-points should be properly selected to avoid unnecessary alarm or shutdown (trip) in transient, but safe, situations.

On the other hand, malfunctions and problems must be identified in their early stages to avoid catastrophic damages. Set-points must be selected case-by-case considering all factors such as machine design, shop-test result, performance-test data, baseline, and so on, but some rules of thumb and practical recommendations may be followed.


Regarding anti-friction bearings, housing vibration (peak to peak) and bearing housing temperature limits are recommended around 10 mm/s and 85 C, respectively. For hydro-dynamic bearings, housing vibration (peak to peak) and bearing housing temperature limits are recommended at around 60 microns and 110 C, respectively (the limits are higher for hydro-dynamic bearings compare to anti-friction).

For anti-friction and hydro-dynamic thrust bearings, axial displacement limits are around 1 mm/s and 0.5 mm, respectively. Lube oil supply and return temperatures are usually around 60 C and 90 C, respectively. Lube oil analysis is an effective tool to evaluate bearing health.

Lube oil viscosity reduction to less than 50 percent (be sure to compare to lube oil producer specification), particle size larger than 25 micron or lube oil water content above 200 ppm need careful attention and can be considered as alarm limits.