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When the fluid flows in the pipe, if the valve close suddenly and
stop the flow, the kinetic energy will be changed into elastic
resilience and create a serial positive and negative pressure wave
vibrating back and forth in the pipe until the energy lost by
friction. Especially when the pump stop, the fluid still flows by
inertia and gravity also cause the fluid to flow back, and these two
forces will cause the positive and negative pressure waves. The
friction caused by the two waves will make the pipe vibrating and
create noise. Hence, the life of the pump and the piping accessories
will be affected and, at the same time, cause the uncomfortable
noise. under such situation, to set up one or more sets of water
hammer arrester will improve the situation.
Our company make use
of the airbag principle to design water hammer arresters which will
reduce the vibration by pressing air when the in-pipe pressure
transfer to air chamber.
The Features of
Water Hammer Arresters :
the airbag adopts the
ball-pressing-type design, which is no friction, less function
progresses, prompt and sensitive response and has obvious
result. In addition, the life of the arrester will be increased
several times.
The arrester will absorb water hammer directly
and has the functions of water hammer prevention and absorption.
Special design of the air diaphragm rubber
will not release pressure and its life won't be affected by the
bad water quality.
To prevent the air leakage, the pressed
air chamber is covered by speeding prevention rubber.
The
design of structure is excellent and easy to maintain.
How big of the fluid pressure of the water hammer
will be?
The water hammer effect caused by
closing the valve should be added at the largest water head in the pipe to calculate the height of the
pressure water head and fluid pressure.
Vensano's
formula:
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Ho = the pressure water
head before closing the valve
Vo = the flow speed before
closing the valve
T = the time needed to close the
valve
L = the pipe length between the inlet and outlet of
free water surface
Zo = the largest pressure water head
increased by water hammer effect
H =full pressure water
head after adding water hammer at the end of the pipe
Remark: the transferring speed of in-pipe pressure and
acceleration
(about 1000 m / second)
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Example GAssume Vo = 5 m/ sec,
Ho = 72 m, L = 210 m, if the it takes 3 seconds to close the valve,
then,what is the pressure of water hammer?
The full
pressure water head including water hammer is H=Zo+H0=71.35+72=143.35 m
Assume the pressure water head 10 m = 1
kgf/cm2
Then, The fluid
pressure including water hammer is 143.35 / 10=14.335 kg .f/cm2 |
