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Table 5: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
Minimum Size Of
Valve
Discharge Pipe
Outlet Size
G1/2
G3/4
G1
Figure 9: Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance Section 3.50)
Safety device
(e.g. Temperature
relief valve)
Discharge pipe (D2) from tundish,
with continuous fall. See Building
18
Minimum Size Of
Discharge Pipe D2
D1
From Tundish
15mm
22mm
28mm
Metal discharge pipe (D1) from
Temperature relief valve to tundish
600mm maximum
300mm
minimum
Regulation G3 section 3.56,
Table 1 and worked example
Maximum Resistance
Allowed, Expressed As A
Length Of Straight Pipe
(I.E. No Elbows Or Bends)
22mm
28mm
35mm
28mm
35mm
42mm
35mm
42mm
54mm
Tundish
Created By Each
Elbow Or Bend
up to 9m
up to 18m
up to 27m
up to 9m
up to 18m
up to 27m
up to 9m
up to 18m
up to 27m
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully
Resistance
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.3m
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