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Water HammersRapidly closing or opening valves may cause
pressure transients in pipelines known as water
hammers
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A Water Hammer is a pressure change caused by a variation of
flow rate in a pipe or tube. Waterhammers arecreated by suddenly
starts or stops o f liquid flows. Since water flows are restricted
inside pipes, shock waves ofincompressible water will travel back
down the pipes def lecting everything on their paths.
The pressure transients in pipes caused by shock waves when
closing or opening valves can be calculated as
dp = 0.070 v l / t (1)
where
dp = increase in pressure (psi)
v = flow velocity (ft/s)
t = valve closing time (s)
l = upstream pipe length (ft)
Example - Water Hammer when Closing Solenoid Valve
The pressure increase in a 100 ftwater pipe where the velocity
is 6 ft/swhen a solenoid valve closes in0.1 scan
be calculated as
dp = 0.070 (5 ft/s) (100 ft) / (0.1 s)
= 350 (psi)
If the solenoid closes in 1 s(solenoid valve with damper) - the
pressure increase is reduced to 35 psi.
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