Page 281 - 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

As can be seen from Figure 5.31, some of the floors below the limit of the mains
cold water supply pressure are supplied un-boosted direct from the cold water
main, with the floors above the mains pressure limit being supplied via the break
cistern and booster set. Drinking water supplies must be from a protected cistern.

Automatic air inlet valve Secondary protection
NOTE: This drawing does not show any additional backflow
prevention devices that may be required under the Water
Supply (Water Fittings) Regulations 1999.
Boosted
mains supply

Limit of mains pressure
To pressure switches
Commpressed air line Pressure gauge

Pneumatic
pressure
vessel
Drain tap Pressure
relief
Break cistern Filtered air vent valve
Incoming supply
Overflow and filter

Pump Un-boosted
stop mains supply
Duplicate
Pump pumps
start
NRV

p
302.06 Figure 5.31 Indirect boosting with pressure vessel
Summary of cold water systems

● In some cases, a combination of both methods of supply may be the best
arrangement. In a dwelling or a house, for example, the ground-floor outlets
and any outside tap could be supplied under mains pressure, while all other
cold water outlet fittings could be fed from a storage cistern.
● The performance of any cold water system is dependent upon the pressure
of the incoming supply and its flow rate.
● Direct systems require a good pressure and flow rate because all of the
appliances use mains cold water supply and, in some cases, mains-fed
instantaneous hot water supply too.
● Indirect cold water systems, where low-pressure supply is used, must be
pipe-sized correctly to ensure that the system meets the design specification
as the lack of pressure is compensated for by an increase in pipe size and,
therefore, flow rate.

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