Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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by Heinz P. Bloch, RE.
Consultanting Engineer
Rolling
Element
Bearings and
Lubrication
Next to mechanical seal failures, bearing failures are most often responsible
for pump outages and repair events. Both rolling element (antifriction)
bearings and sliding element (plain) bearings are used in centrifugal
pumps. Each of these two bearing categories is found in small as
well as large and in single as well as multistage pumps. However, very
large or very high speed pumps tend to favor sliding element bearings
over rolling element bearings.
Because the preponderance of centrifugal pumps is small, say less than
200 hp (~ 150 kW), most pumps are equipped with rolling element bearings.
Avoiding or reducing rolling element bearing failures should thus
be a prime topic whenever pump life extensions are being discussed.
A rolling element bearing is a precision device and a marvel of engineering.
It is unlikely that any other mass-produced item is machined to
such close tolerances. While boundary dimensions are usually held to
tenths of a thousandth of an inch, rolling contact surfaces and geometries
are maintained to millionths of an inch. It is for this obvious reason that
very little surface degeneration can be tolerated [12],
The life of a rolling element bearing running under good operating
conditions is usually limited by fatigue failure rather than by wear. Under
optimum operating conditions, the fatigue life of a bearing is determined
by the number of stress reversals and by the cube of the load causing
these stresses. As example, if the load on the bearing is doubled, the the-
* Material on lubrication of rolling element bearings adapted by permission from TRW Bearings Division,
Jamestown, New York,
524