17
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 Straight Pipe (I.E.
No Elbows Or Bends)
Resistance Created
By Each Elbow Or
Bend
G1/2
15mm
22mm
28mm
35mm
up to 9m
up to 18m
up to 27m
0.8m
1.0m
1.4m
G3/4
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 5: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
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
600mm
maximum
300
mm
minimum
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.56,
Table 5 and worked example
Figure 10: Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance Section 3.50)
