Why Bearings Fail and How to Prevent Bearing Failures

Source: https://imgur.com/SbQmvhJ

Bearings are a crucial component for centrifugal pumps. As to be expected, bearings cannot last forever in a centrifugal pump, and eventually, bearings will fail. “This is because pump bearings usually fail from causes other than fatigue”1. These causes of bearing failure vary greatly, however, the reasons include “excessive thrust, misalignment, inadequate lubrication, impact, static vibration, insufficient loading and contamination”2 Keep in mind that inadequate lubrication includes too little lubrication, the wrong type of lubricant as well as too much lubrication: For too much lubrication on bearings can actually lead to overheating.

It is also important to thoroughly analyze bearing failures. “Even if the cost of the bearing is small, the direct and indirect associated costs of its failure and replacement can be substantial. For example, a pump bearing may only cost $20 to buy, but its failure could also take out a mechanical seal.”3 Because of the potential consequences of further failures to parts of the pump, great attention to detail must be taken when observing causes of failure to a pump.

For example, a chain of destruction to a centrifugal pump’s parts can occur just because of a bearing seal, such as a lip seal: “When the rubber lip can no longer maintain contact with the spinning shaft, the oil or grease can leak out of the bearing housing. Contaminants can enter into and destroy the bearings. When the lip seal is changed with the bearing change, the new lip rides into the old groove cut by the previous lip. That’s how a $6-dollar rubber lip seal can take out a $300.00 bearing and an $800.00 stainless steel pump shaft”4 This is a horrific consequence of a bearing seal failure, and yet what is worse is that if the root cause of bearing seal failures isn’t addressed, then the bearing seal will continue to fail throughout the year and result in great cost of repairs.

The most effective method of preventing bearing failures is regular, scheduled maintenance and proper installation. For example, a lip seal is designed to run for about 2,000 hours, which is equivalent to 83 (eighty-three) days. Once beyond its designed lifespan of 2,000 hours, the shaft will burn the lip itself or the lip will begin to destroy the shaft. Another effective measure to prevent bearings from failing before their designed life cycle ends is to adequately lubricate the bearings according to manufacturer specifications. Further methods of preventing bearing failure can be taken by means of great care and caution when installing bearings.

It is also advised to prevent a bearing from contamination, which means avoiding touching the bearing itself, as well as avoiding leaving the bearing exposed overnight or allowing compressed air to come into contact with the bearing, for all of these can cause bearing contamination. Keep in mind that, although with too much lubrication resulting in overheating, “Bearings can operate safely in the 200°F range”5 and are “perfectly safe at 160°F. This is actually good for a bearing because of the expected lubricant flow at this temperature.”6 The best practices for avoiding bearing failure are great care and caution when installing a bearing in a centrifugal pump, as well as referring to the user manual, and inquiry to the bearing manufacturer when major uncertainties arise.

  1. https://www.skf.com/us/products/mrc/bearings-for-pumps
  2. Same as 1
  3. Bachus, Know and Understand Centrifugal Pumps p.159-160
  4. Same as 3
  5. Same as 3
  6. Same as 3