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

550 Centrifugal Pumps: Design and Application
Figure 20*17. Percent failure vs. hours to leakage for two types of lip seals
(courtesy of L. A. Horve, "CR Waveseal—A Detailed Synopsis of Five Comparative
Life Tests").
API-type pumps are generally furnished with non-contacting labyrinth
seals or bearing isolators similar to the one depicted in Figure 20-18.
However, neither of these two executions can claim to represent a totally
effective barrier against the intrusion of atmospheric dust or moisture.
Moisture, in particular, can cause unexpectedly high decreases in bearing
fatigue life. Armstrong and Murphy [1] summarize the deleterious effects
of water in lube oil. They state that in the 1960s, researchers Grunberg
and Scott had found the fatigue life at a water content of 0.002%
reduced 48% and, at 6.0% water, found it to be reduced 83%. Others
found a fatigue life reduction of 32% to 43% for squalene containing
0.01 % water, and a third group of researchers detected about an 80%
drop with a moist air environment contacting dried mineral oil (see Table
20-3). While the detailed mechanism for the reduction of fatigue life by
water in a lubricant is not completely understood, it is thought to relate to
aqueous corrosion. There is much evidence that the water breaks down
and liberates atomic hydrogen. This causes hydrogen embrittlement and
increases the rate of cracking of the bearing material by a significant
margin.
A solution to the problem of sealing pump-bearing housings can be
found in aircraft and aerospace hydraulic pumps, which make extensive
use of magnetic face seals. This simple seal consists of two basic compo-