Page 92 - Root Cause Failure Analysis

Pumps 83
i

f

I I

Figure 7-4 Pumps in parallel may share suction supply.

as air or steam, has an adverse effect on both the pump’s efficiency and its useful
operating life. This is one form of cavitation, which is a common failure mode of cen-
trifugal pumps. The typical causes of cavitation are leaks in suction piping and valves,
or a change of phase induced by liquid temperature or suction pressure deviations. As
an example, a one-pound suction pressure change in a boiler-feed application may
permit the deaerator-supplied water to flash into steam. The introduction of a two-
phase mixture of hot water and steam into the pump causes accelerated wear, instabil-
ity, loss of pump performance, and chronic failure problems.