TM 5-813-9
4-2. Pump Cavitation.
will not be a problem in a pump installation if the
system is designed, selected, installed, and operated
a. Cavitation is a term used to describe a
in accordance with the recommendations of the
phenomenon that may occur in a pumping instal-
designer and the manufacturer.
lation and may occur in piping systems because of
liquid velocity changes. Cavitation in centrifugal
4-3. Surge Analysis
pumps is explained in TM 5-813-5. Cavitation in
a. General. Surges in pipelines carrying liquids
pipe lines may take place at sudden enlargements of
are usually caused by opening, closing or regulating
the pipe cross section, at sharp bends, throttled
valves or pumps starting and stopping. These
valves or similar situations. The designer should
surges, also called hydraulic transients may range in
avoid the following conditions for centrifugal
importance from a slight pressure or velocity
pumps:
change to sufficiently high pressure or vacuum to
(1) Operating heads much lower than rated
rupture the piping system, to damage pumping
head at peak efficiency of the pump.
equipment and cause extensive shutdown time.
(2) Operating capacities much higher than rated
Water hammer, a result of hydraulic transients, will
capacity at peak efficiency of the pump.
occur when the total surge pressure exceeds
(3) Suction lift higher or positive suction head
approximately twice the value of the static pressure
lower than recommended by the manufacturer.
in the system when the fluid is at rest. "Water
(4) Liquid temperatures higher than that for
hammer" is discussed in TM 5-813-5. Surge
which the system was originally designed.
protection analysis will be performed on critical
(5) Pump speeds higher than manufacturer's
sections of the piping system to verify design and
recommendations.
surge control equipment selection. If excess
transient pressures are predicted by the analysis,
avoid these conditions except conditions (1) and (2)
design and mechanical equipment application will
will be stated as follows:
be modified. Hydraulic surge control is a
(1) Operating heads much higher than peak
specialized field. If a detailed surge protection
efficiency of the pump.
study is required, it should be provided by engi-
(2) Operating capacities much lower than ca-
neers or consulting engineering firms specialized in
pacity at peak efficiency of the pump. Cavitation
this field. Detailed pipeline surge analysis by an
4-3
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