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

Rolling Element Bearings and Lubrications 543
Figure 20-11. Multi-stage pump and electric motor connected to oil mist tubing
(courtesy of Lubrication Systems Company, Houston, Texas).
• The need for periodic oil changes is eliminated.
• Long-term oil breakdown, oil sludge formation, and oil contamination
are no longer factors affecting bearing life.
» The ingress of atmospheric moisture into the motor bearing is no
longer possible and even the bearings of standby equipment are properly
preserved. Without oil mist application, daily solar heating and
nightly cooling cause air in the bearing housing to expand and contract.
This allows humid, often dusty air to be drawn into the housing with
each thermal cycle. The effect of moisture condensation on rolling element
bearings is extremely detrimental and is chiefly responsible for
few bearings ever seeing their design life expectancy in a conventionally
lubricated environment.
It has been established that loss of mist to a pump or motor is not likely
to cause an immediate and catastrophic bearing failure. Tests by various
oil mist users have proven that bearings operating within their load and
temperature limits can continue to operate without problems for periods
in excess of eight hours. Furthermore, experience with properly maintained
oil mist systems has demonstrated outstanding service factors. Because
there are no moving parts in the basic oil mist components, and