As observant equipment maintenance and reliability professionals know, some oil-lubricated bearings have their lube oil levels set to reach the center of the lowermost ("6 o-clock") rolling element.  Allowing lube oil to reach the center of the lowermost bearing ball of, say, a 70 mm bearing is acceptable at 1,500 and 1,800 rpm.  So, why are there still oil rings in some of those bearing housings if, in fact, the oil covers one-half of the lowermost rolling element?

There was a time when people did failure analysis by guessing at the cause and trying something different.  The result:  repeat failures; the same machine ending up in the shop time after time.  Today, we no longer can afford to guess.  A structured repeatable approach is needed.

The Basics

Mechanical seals are leakage control devices, which are found on rotating equipment such as pumps and mixers to prevent the leakage of liquids and gases from escaping into the environment. Figure below shows a typical centrifugal pump, which highlights its constituent parts, including the mechanical seal.

More bearing failures are lube-related than load related. The following pie chart tells the story better than words; it displays issues relating to both oil and grease lubrication at a US oil refinery.

        

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