andrews BUFFER-GL200-8 Installation And Service Manual page 14

The following extract is taken from latest G3 Regulations
Discharge pipes from safety
Devices Discharge pipe D1
3.50 Safety devices such as temperature relief valves or combined temperature and
pres- sure relief valves (see paragraphs 3.13 or 3.18) should discharge either directly or by
way of a manifold via a short length of metal pipe (D1) to a tundish.
3.51 The diameter of discharge pipe (D1) should be not less than the nominal outlet size of
the safety device, e.g. temperature relief valve.
3.52 Where a manifold is used it should be sized to accept and discharge the total discharge
from the discharge pipes connected to it.
3.53 Where valves other than a temperature and pressure relief valve from a single
unvented hot water system discharge by way of the same manifold that is used by the safety
devices, the manifold should be factory fitted as part of the hot water storage system unit
or package.
Tundish
3.54 The tundish should be vertical, located in the same space as the unvented hot water
stor- age system and be fitted as close as possible to, and lower than, the safety device, with
no more than 600mm of pipe between the valve outlet and the tundish (see Diagram 1).
Note: To comply with the Water Supply (Water Fittings) Regulations, the tundish should
incorpo- rate a suitable air gap.
3.55 Any discharge should be visible at the tundish. In addition, where discharges from
safety devices may not be apparent, e.g. in dwellings occupied by people with impaired
vision or mo- bility, consideration should be given to the installation of a suitable safety
device to warn when discharge takes place, e.g. electronically operated.
Discharge pipe D2
3.56 The discharge pipe (D2) from the tundish should:
a. have a vertical section of pipe at least 300mm long below the tundish before any elbows
or bends in the pipework (see Diagram 1); and
b. be installed with a continuous fall of at least 1 in 200 thereafter.
3.57 The discharge pipe (D2) should be made of:
a. metal; or
b. other material that has been demonstrated to be capable of safely withstanding
temperatures of the water discharged and is clearly and permanently marked to identify the
product and per- formance standard (e.g. as specified in the relevant part of BS 7291-
1:2006 Thermostatic pipes and fittings for hot and cold water for domestic purposes and
heating installations in buildings. General requirements).
3.58 The discharge pipe D2 should be at least one pipe size larger than the nominal outlet
size of the safety device unless its total equivalent hydraulic resistance exceeds that of a
straight pipe 9m long, i.e. for discharge pipes between 9m and 18m the equivalent resistance
length should be at least two sizes larger than the nominal outlet size of the safety device;
between 18 and 27m at least 3 sizes larger, and so on; bends must be taken into account in
calculating the flow resistance. See Diagram 1, Table 3.1 and the worked example.
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