Issue 1 06/02/20
25
Installation
6
Therefore the permitted length equates to: 5.8m
5.8m is less than the actual length of 7m therefore calculate the
next largest size.
Maximum resistance allowed for a straight length of 28mm pipe
(D2) from a G1/2 temperature relief valves equates to 18m.
Subtract the resistance of 4 No. 28mm elbows at 1.0m each =
4.0m
Therefore the maximum permitted length equates to: 14m
As the actual length is 7m, a 28mm (D2) copper pipe will be
satisfactory.
Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
Valve Minimum Size Of Minimum Size Of Maximum Resistance Resistance Created By
Outlet Size Discharge Pipe D1 Discharge Pipe D2 Allowed, Expressed As Each Elbow Or Bend
From Tundish A Length Of Straight Pipe
(I.E. No Elbows Or Bends)
22mm up to 9m 0.8m
G1/2 15mm 28mm up to 18m 1.0m
35mm up to 27m 1.4m
28mm up to 9m 1.0m
G3/4 22mm 35mm up to 18m 1.4m
42mm up to 27m 1.7m
35mm up to 9m 1.4m
G1 28mm 42mm up to 18m 1.7m
54mm up to 27m 2.3m
Fig. 13
Table 6
Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance Section 3.50)
Safety device
(e.g. temperature
relief valve)
Metal discharge pipe (D1) from
temperature relief valve to tundish
Tundish
600mm maximum
Fixed grating
Trapped
gully
Discharge below fixed
grating (building regulation
G3 section 3.61 gives
alternative points of
discharge)
Discharge pipe (D2) from tundish, with
continuous fall. See building regulations G3
section 3.56, Table 1 and worked example
300mm
minimum
