Problem: The use of single-row angular contact bearings has increased considerably over the past few decades, but are they being installed properly in the pumps in your plant?
This bearing is designed to support a heavy thrust load in one direction only. It can also handle a moderate radial load. The contact angle is achieved by a high shoulder on the inner ring and another high shoulder, diametrally opposite, on the outer ring.
This design is usually used as matched pairs of single-row bearings, but it must be noted that these are usually matched in production so that an even distribution of the load can be achieved without the use of shims. Solution: Three alternative arrangements of the double angular contact bearings are possible and the bearings must be properly arranged so that the load lines will handle the anticipated direction of the thrust loads.
The Tandem arrangement has the load lines in parallel and the pair can accommodate axial loads in one direction only. This is generally not a problem as it is easy to identify during installation, with the high shoulders being on the same side in both bearings.
If, however, the load from the pump can change from one direction to the other, both the other two arrangements can handle such a condition; the Face to Face and the Back to Back. Consequently, we have the frequent question, "Is there a right and wrong way to install these two?" Many suppliers will tell you that it doesn't matter; unfortunately, that is not always the case.
The Back to Back arrangement has the facility of handling any tilting moments that may be developed from shaft misalignment difficulties, and therefore is the preferred arrangement on end suction pumps where the thrust bearing is adjacent to the shaft coupling.
Although it is not critical in double-ended pumps, where the thrust bearing is at the other end of the shaft from the coupling, it is still a good idea to instil a constancy of application with these bearings. So always install the double row angular contact bearings in the Back to Back arrangement
Mr. O's thanks for this tip go to Ross Mackay, an internationally recognized specialist in pumping reliability. He is a graduate in mechanical engineering from Stow College of Engineering in Glasgow, Scotland. For more tips, visit practicalpumping.com.
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