Page 361 - 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 6 Hot water systems

SECTION 8
Schedule 2: Paragraphs 17, 18, 19,
20, 21, 22, 23 and 24: Hot water
services Guidance
G19.3 The discharge pipe from a temperature relief valve or combined temperature and
pressure relief valve should:
a Be through a readily visible air gap discharging over a tundish located in the same
room or internal space and vertically as near as possible and in any case within 600
mm of the point of outlet of the valve; and,
b Be of non-ferrous material, such as copper or stainless steel, capable of withstanding
any temperatures arising from a malfunction of the system; and,
c Have a vertical drop of 300 mm below the tundish outlet, and thereafter be laid to a
self-draining gradient; and,
d Be at least one size larger than the nominal outlet size of the valve, unless its total
equivalent hydraulic resistance exceeds that of a straight pipe 9 metres long. Where
the total length of the pipe exceeds 9 metres equivalent resistance, the pipe shall be
increased in size by one nominal diameter for each additional, or part of, equivalent
9 metres resistance length. The flow resistance of bends in the pipe should be taken
into consideration when determining the equivalent length of pipe; and,
e Terminate in a safe place where there is no risk to persons in the vicinity of the point
of discharge. See Building Regulation G3.
Note: Alternatively, the size of the discharge pipe may be determined in accordance
with Annex D of BS 6700.
Discharge pipes from expansion valves
G19.4 The discharge pipe from an expansion valve may discharge into the tundish used
for the discharge from a temperature relief valve or from a combined temperature and
pressure relief valve as described in G19.1; or:
a Discharge through a readily visible air gap over a tundish located in the same room
or internal space and vertically as near as possible and in any case within 600 mm of
the point of outlet of the valve; and,
b Be of non-ferrous material, such as copper or stainless steel; and,
c Discharge from the tundish through a vertical drop outlet and thereafter be laid to a
self draining gradient; and,
d Not be less than the nominal outlet size of the expansion valve and discharge external
to the building at a safe and visible location.
20 (1) No vent pipe from a primary Vent pipes
circuit shall terminate over a storage G20.1 Vent pipes from primary water systems should be of adequate size but not less
cistern containing wholesome water for than 19 mm internal diameter. They may terminate over their respective cold water
domestic supply or for supplying water feed and expansion cisterns, or elsewhere providing there is a physical air gap, at least
to a secondary system. equivalent to the size of the vent pipe, above the top of the warning pipe, or overflow if
(2) No vent pipe from a secondary there is one, at the point of termination.
circuit shall terminate over any G20.2 Vent pipes from hot water secondary storage systems should be of adequate size
combined feed and expansion cistern but not less than 19 mm internal diameter and be insulated against freezing.
connected to a primary circuit.
G20.3 Where vent pipes, from either a primary or secondary system, terminate over
their respective cold water feed cisterns, they should rise to a height above the top water
level in the cistern sufficient to prevent any discharge occurring under normal operating
conditions.
Hot water systems supplied with water from storage cisterns
G20.4 In any cistern-fed vented or unvented hot water storage system the storage vessel
should:
a be capable of accommodating any expansion water; or
b be connected to a separate expansion cistern or vessel; or
c be so arranged that expansion water can pass back through a feed pipe to the cold
water storage cistern from which the apparatus or cylinder is supplied with water.
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