Angular Contact Bearings
The use of angular contact bearings has increased considerably during recent years, but when used in a double arrangement, are they being installed properly in your pumps...?
This question came to my attention some time ago when discussing a wider view of bearings with a client, and it revealed some surprising information that he was being told by a bearing supplier. Further research revealed that the same misinformation was fairly widespread from other bearing houses across the country. But first, let’s review the arrangements in question....
The single angular contact 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 so that an even distribution of the load can be achieved.
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 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 Face to Face and Back to Back arrangements can handle such a condition. Consequently, we have the frequent question, “Is there a right way to install them?”
Many bearing house suppliers will tell you that it doesn’t matter, but that is not always the case.
It is worthwhile to recognize that the Back to Back arrangement provides a greater angular rigidity and is a much better arrangement for accepting tilting moments that may result from shaft misalignment difficulties, and are more prevalent in end suction pumps where the thrust bearing is located beside the shaft coupling.
Therefore, the Back to Back arrangement must always be used in end suction pumps.
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 a good idea to instill a constancy of application with these bearings. So always install the double row angular contact bearings in the Back to Back arrangement.
Author of “The Practical Pumping Handbook” and a specialistr in Pumping Reliability, Ross Mackay can be reached at www.practicalpumping.com or at 1-800-465-6260