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9
VALVE OUTLET
SIZE
MINIMUM SIZE
OF DISCHARGE
PIPE D1
MINIMUM SIZE
OF DISCHARGE
PIPR D2 FROM
TUNDISH
MAXIMUM
RESISTANCE
ALLOWED,
EXPRESSED AS
A LENGTH OF
STRAIGHT PIPE
(I.E. NO ELBOWS
OR BENDS)
RESISTANCE
CREATED BY
EACH ELBOW OR
BEND
G 1/2
15mm
22mm
28mm
35mm
UP TO 9M
UP TO 18M
UP TO 27M
0.8M
1.0M
1.4M
G 3/4
22mm
28mm
35mm
42mm
UP TO 9M
UP TO 18M
UP TO 27M
1.0M
1.4M
1.7M
G1
28mm
35mm
42mm
54mm
UP TO 9M
UP TO 18M
UP TO 27M
1.4M
1.7M
2.3M
Table 3: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
NOTE:
The above table is based on copper tube. 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.
600mm maximum
300mm
minimum
Safety device
(e.g. Temperature
relief valve)
Metal discharge pipe (D1) from
Temperature relief valve to tundish
Tundish
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully
Discharge pipe (D2 from tundish,
with continuous fall. See Building
Regulation G3 section 3.55,
Table 4 and worked example
Fig. 5: Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance section 3.5