andrews STOR-SS300-8-S Installation And Service Manual page 25

Table 6
Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
Valve Minimum Size Of
Outlet Size Discharge Pipe D1
G1/2
G3/4
G1
Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance Section 3.50)
Fig. 13
Safety device
(e.g. temperature
relief valve)
Discharge pipe (D2) from tundish, with
continuous fall. See building regulations G3
section 3.56, Table 1 and worked example
Issue 1 06/02/20
Minimum Size Of
Discharge Pipe D2
From Tundish
22mm
15mm 28mm
35mm
28mm
22mm 35mm
42mm
35mm
28mm 42mm
54mm
Metal discharge pipe (D1) from
temperature relief valve to tundish
600mm maximum
300mm
minimum
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.
Maximum Resistance
Allowed, Expressed As
A Length Of Straight Pipe
(I.E. No Elbows Or Bends)
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
Tundish
Installation
Resistance Created By
Each Elbow Or Bend
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.3m
Discharge below fixed
grating (building regulation
G3 section 3.61 gives
alternative points of
discharge)
Fixed grating
Trapped
gully
6
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