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DESIGN: DEAR MR PLUMBER
Maximum pressure for
municipality water connection
An engineer friend phoned and asked me, “What is
the maximum pressure that the municipality’s water
connection is supposed to be?”
By Vollie Brink, Pr Eng
My answer was, “900kPa as per the national model
by-laws, but these model by-laws also state that the
water connection is provided under three conditions,
which are: no guarantee of water, no guarantee of
pressure, and no guarantee of quality, and it is taken
up in the local water by-laws of the municipalities.”
Vollie Brink
Vollie Brink is one of the
industry’s longest serving
wet service engineers.
He continues to serve on
SABS committees and
has been involved in the
Green Building Council
Star rating system.
Brink continues to consult
for various organisations
while enjoying a
well-earned retirement.
My engineer friend also complained that the municipality
worked on the water supply piping near his house and
when they re-opened the valves too quickly, it caused
massive water hammer and a surge of high pressure
— above 900kPa — at his house. I have received
numerous complaints about very high municipal water
pressures during night-time and in some cases, the
pressure went up to 20 bar, causing damage.
Although the municipality is not allowed to give you water
at a higher pressure than 900kPa, they are ‘covered’
by the fact that they do not have to guarantee a specific
pressure. On the one hand it is a problem, but on the
other hand one must be thankful to have water, even at a
non-guaranteed pressure.
I had a case where a municipality worked on the water
supply piping during the night and they raised the
pressure to be able to supply water. When the work was
done, they opened the valves too quickly and a huge
wave of water caused about 2km of piping to be pulled
off the slab in the basement. Fortunately, it was night-
time and there were no cars parked or people.
The piping was ‘protected’ with a PRV but it still came
through and caused severe damage. I now propagate
that all such installations be protected by a PRV, and
also by a water hammer arrester as a safety precaution.
Some PRV valves have a built-in water hammer arrester.
The design and construction of a building water
installation is ‘dictated’ by the three municipal water
supply conditions and it is the responsibility of the owner
to accept it ‘as is’, or to secure it by means of technical
solutions and engineering design.
Water hammer can cause serious problems, damage,
and is a safety threat. It must be addressed in the
design. It is essential to train facilities management
services, plumbers, and their assistants, to slowly
open and close water supply valves to prevent
water hammer.
Other fixtures that cause water hammer are the solenoid
valve that you find in a kitchen canopy and the one that you
find in the water supply to an irrigation system, and also
where there is a small pump that suddenly starts and stops.
It has also been found that water hammer is created by
a certain water meter. Water hammer can cause serious
damage to water piping with spigot and socket plastic
piping, even when the piping is more than one-meter
deep underground.
I had a case where a small pump in a factory started
and stopped suddenly and caused huge surges of
water hammer in a 300mm-diameter pipe one-meter
underground and after six months, the joints were worn
out and the piping had to be replaced.
It is recommended that the flow velocity in a pipe in a
building above ground should be around one to 1.5m/
second to prevent noise and water hammer.
Please note that water hammer is not a hammer you can
purchase at the hardware shop (just a little joke). PA
WHAT IS A WATER HAMMER ARRESTER?
When a valve closes quickly and stops the flow, that momentum shakes and pounds pipes. Water hammer
arresters cure this condition with a cushion of air that absorbs the momentum. Before you install arresters,
determine which faucets or valves in your house cause the noise.
September 2018 Volume 24 I Number 7
www.plumbingafrica.co.za