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............................... Pump Bearings

7.9.1 Sealed bearings
When available in deep groove ~iiiiiiiiiiiiiiiiiililiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii~
and double row styles, sealed
bearings may be appropriate.
These bearings are fitted with two
seals and are not regreasable. They
are considered 'sealed for life' (the
life of the bearing). In these
conditions the bearing cavity is
filled to approximately 25% to 35%
with grease. This offers a good
guide to those who have a Figure 7.17: Sealed bearing
tendency to over-grease bearings.
However, the life expectancy of the bearings still depends on the L-10
fatigue life of the bearing and the quality of the grease.

7.9.2 The lip seal
The most commonly used device to keep contaminants out of the
beating housing is the lip seal, in spite of the fact that it has long been
proved to be inappropriate for it's intended function in a centrifugal
process pump. It should be noted for the purposes of clarification that,
the function of the seal in the bearing housing is to keep contaminants
out of the housing, and not to keep the lubricant in the housing.
The lip seal is designed for the equivalent of an L-10 life of 1,000
operating hours. In a pump operating on continuous duty, that
translates into a period of less than 6 weeks. This life span is also
dependent on the lip seal being well lubricated, yet most process pumps

m

Figure 7.18: Typical lip seal

121 J