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

Rolling Element Bearings and Lubrications 53?
a centrifugal pump. However, unless frictional heat generated by the
bearing is readily dissipated, the lubricating oil must serve also as a coolant,
The MRC Bearing Division of TRW calculates the theoretical oil flow
required for cooling from the expression.
where
Fr = Coefficient of friction referred to PD
.00076 = cylindrical roller bearings
.00089 = pure thrust ball bearings
.00103 = radial ball bearings
.00152 = angular contact ball bearings
.002-.005 = tapered roller bearings
P = imposed equivalent load in pounds
PD = pitch diameter in inches
RPM = operating speed in revolutions per minutes
T 0 = outlet oil temperature in °F
Tj = inlet oil temperature in °F (T 0 - Tj, generally about
50°F)
H s = specific heat of oil in BTU/LB/°F (usually .46 - .48)
= . 195 + .000478 (460 + Tj)
Conversion: (pounds of oil per minute) x (0.135) = gal/min
Hence, where cooling is required in high speed and heavily loaded
bearings, oil jets and circulating systems should be considered. If necessary,
the oil can be passed through a heat exchanger before returning to
the bearing.
Oil Bath Lubrication
A simple oil bath method is satisfactory for low and moderate speeds.
The static oil level should not exceed the center line of the lowermost ball
or roller. A greater amount of oil can cause churning that results in abnormally
high operating temperatures. Systems of this type generally
employ sight gauges to facilitate inspection of the oil level.
Figure 20-4 shows a constant level arrangement for maintaining the
correct oil level. Figure 20-5 shows a similar arrangement that includes a
pressure-balanced constant level oiler.