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MINIMUM
VALVE
SIZE OF
OUTLET
DISCHARGE
SIZE
PIPE D1
G1/2
15 mm
G3/4
22 mm
G1
28 mm
Table 4: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
NOTE: The table below is based on copper pipe. Plastic pipes may be of different bore and resistance. Sizes and
maximum lengths of plastic should be calculated using data prepared for the type of pipe being used.
Safety device
(e.g. Temperature
relief valve)
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.56,
Table 1 and worked example
Fig. 4: Typical Discharge Pipe Arrangement (Extract from building regulation G3 guidance section 3.50)
10
MINIMUM SIZE OF
DISCHARGE PIPE
D2 FROM TUNDISH
22 mm
28 mm
35 mm
28 mm
35 mm
42 mm
35 mm
42 mm
54 mm
Metal discharge pipe (D1) from
Temperature relief valve to tundish
600 mm maximum
300 mm
minimum
MAXIMUM RESISTANCE
ALLOWED,
EXPRESSED AS A
LENGTH OF STRAIGHT
PIPE
(I.E. NO ELBOWS
OR BENDS)
UP TO 9 m
UP TO 18 m
UP TO 27 m
UP TO 9 m
UP TO 18 m
UP TO 27 m
UP TO 9 m
UP TO 18 m
UP TO 27 m
Tundish
RESISTANCE
CREATED BY
EACH ELBOW
OR BEND
0.8 m
1.0 m
1.4 m
1.0 m
1.4 m
1.7 m
1.4 m
1.7 m
2.3 m
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully
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