Page 341 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 5 Cold water systems

Noise

System noise can take many forms, from a squealing tap washer to violent
pipework reverberation and water hammer. Most noise within direct systems
of cold water is a direct result of the high pressure and flow rate that can occur
within this system. It should be remembered that whenever a system has a
mixture of high pressure and high flow rate, there will always be a certain
amount of noise within that system. Sometimes, however, the noise can be
excessive and this may be attributable to:
● Faulty tap washers: these tend to make a humming or squealing noise when
the tap is opened. It is usually because the tap washer is either worn or split,
and re-washering the tap cures the problem in most cases.
● Faulty FOV washers: this can cause a very loud hum throughout the
pipework. Unfortunately, the noise is amplified if the cistern is in the roof
space. Re-washering the FOV generally cures the fault. One way of testing to
see if it is the FOV washer is to turn on a cold tap when the noise begins. If
the noise stops or goes quieter, it is probably the FOV washer.
● Loose or incorrectly supported pipework: this can be the cause of very
violent banging within the system. Every time the pipework reverberates,
it is equal to twice the incoming mains pressure. If the supply is at 3 bar,
then each bang is the equivalent of 6 bar. This can eventually lead to fittings
failure and leakage. The best course of action is to try to find where the
pipework is loose, and re-fix it. If this is not possible, the installation of a
water hammer arrester fitted near to the main stop valve inside the property
may cure the problem.

Inadequate water supply

Airlocks on low-pressure systems can be a constant nuisance, especially during
the commissioning stage. Airlocks stop the flow of water due to air trapped in
the pipework, and there is insufficient water pressure from the cistern to push
the air out. They usually occur because the cold distribution pipe rises as it
leaves the cistern rather than falling towards the appliances, and this causes a
high spot where air collects. It is often a result of poor installation or design.

Curing an airlock is not easy. Usually, the best course of action is to leave the
system to settle. Most airlocks eventually move, allowing water to flow. This can
be problematic if the system is new and at the commissioning stage, because
the system cannot be tested properly until the airlock clears. To be sure that
airlocks do not occur, ensure that distribution pipes from cisterns have a slight
but constant fall towards the appliances.

Leakage
Leakage is a common problem in cold water systems. It can take three main forms:

● Leakage from the cold water service pipe below ground before it enters the
property: this is quite difficult to detect. The main signs of leakage are loss of
water pressure and flow rate and a constant distant sound of running water. To
find out whether the leak is before or after the external (boundary) stop valve,
the external stop valve must be turned off; if the water supply has stopped but
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