10 / EN
iv) Where a single pipe serves a number of discharges, such as in blocks of fl ats, the number served
should be limited to no more than 6 systems so that any installation can be traced reasonably easily.
The single common discharge pipe should be at least one pipe size large than the largest individual
discharge pipe to be connected. If unvented hot water storage systems are installed where discharg-
es from safety devices may not be apparent i.e. in dwellings occupied by the blind, infi rm or disabled
people, consideration should be given to the installation of an electronically operated device to warn
when discharge takes place. Note: The discharge will consist of scalding water and steam.
Asphalt, roofi ng felt and non-metallic rainwater goods may be damaged by such discharges.
Table 2
Sizing of copper discharge pipe “D2” for common temperature valve outlets
Valve
outlet size
Minimum
size of
discharge
pipe D1*
Minimum size of
discharge pipe
D2* from tundish
Maximum resistance
allowed, expressed as
a length of pipe
(i.e. no elbow or bends)
Resistance created
by each elbow or
bend
G 1/2 15 mm 22 mm
28 mm
35 mm
Up to 9 m
Up to 18 m
Up to 27 m
0.8 m
1.0 m
1.4 m
G 3/4 22 mm 28 mm
35 mm
42 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.0 m
1.4 m
1.7 m
G 1 28 mm 35 mm
42 mm
54 mm
Up to 9 m
Up to 18 m
Up to 27 m
1.4 m
1.7 m
2.3 m
600 mm Max.
300 mm
Min.
Temperature & pressure
relief valve
Metal discharge pipe (D1) from
temperature & pressure relief valve.
to tundish.
Metal discharge pipe (D2) from tundish
with continuous fall. See Table 2 and worked
example.
Tundish
Fixed grating
Trapped gulley
Discharge below
fixed grating.
(see page 6 for
alternative points
of discharge).
Suggest ways of terminating discharge pipes safely
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