Page 275 - 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

The cistern should be installed as high as possible to increase the system pressure.

230–250 litre storage cistern fitted with
BS 1212 part 2 float-operated valve
Spherical ball-type
service valve

22 mm or 28mm cold WC cistern fitted with
feed to secondary either a BS 1212 part 2,
hot water cylinder part 3 or part 4 float-
22 mm or 28mm full way operated valve
gate valve or lever-type
spherical ball valve
Spherical ball-type
service valve

22 mm cold distribution pipework to the bath
reducing to 15mm to feed the wash hand basin
and WC cistern
Drain-off valves

p Figure 5.25 The indirect system of cold water supply

Pipe sizes for the indirect system
Pipe size depends on the system design but, generally speaking:
● a 15 mm rising cold water main will be large enough to supply most cold
water demands for a three- to four-bedroom house
● the kitchen sink should be supplied with water direct from the cold water
main and 15 mm pipework is adequate for this; the cold water storage cistern
can also be supplied via 15 mm pipework
● a cold water distribution pipe (22 mm minimum) distributes cold water from
the cistern to the washbasin, WC and bath; the bath should be supplied from
22 mm pipework because of the lack of pressure, but all other appliances can
effectively be supplied from 15 mm pipework
● a 28 mm (22 mm minimum) cold feed pipe is needed to supply the hot water
storage vessel; this system is ideal when mixing valves and taps require equal
pressure and flow rate as both hot and cold supplies are fed from the same
source, this being the cold water storage cistern.
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