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VACUUM
BREAKERS IN FIREWATER SYSTEMS
1. Description:
Vacuum Breaker Valves
It was suggested that installing
vacuum breaker/air release
valves at the high points in the
system was one way of
controlling pressure surges
arising due to cavity
separation.
The scenario is as follows. The
clack open deluge valve receives
a signal to open, and opens
because it is actuated by
instrument air or some other
means. The fire pump receives a
signal to start at the same
time. However, it takes time for
the fire pump to prime the
caisson and during that time it
is unable to maintain the
pressure in the ringmain. This
would result in vacuum pressures
developing in the higher parts
of the system which could lead
to cavity formation.
Vacuum breaker/air release
valves are often used to counter
this cavity formation. Basically
before the fire pump has primed
they allow air to come into the
system fast so that the pressure
at the higher levels of the
ringmain remain near atmospheric
pressure. When the pump has
primed the system the air
release valve, which is a much
smaller valve, allows the
ingressed air to go out
relatively slowly. It is
important that the air release
valve is small, otherwise water
can move up the riser pipe very
fast and this can create a surge
when it reaches the air release
valve and closes it.
2. Typical Arrangement:
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