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3.63 – The discharge would consist of high
`
temperature water and steam. Asphalt, roofing
felt and non-metallic rainwater goods may be
damaged by such discharges.
Worked example of discharge pipe sizing
`
Fig. 15: shows a G1/2 temperature relief valve
`
with a discharge pipe (D2) having 4 No. elbows
and length of 7m from the tundish to the point
of discharge.
From Table 5:
`
Maximum resistance allowed for a straight
`
length of 22mm copper discharge pipe (D2) from
a G1/2
temperature relief valve is 9.0m.
`
Subtract the resistance for 4 No. 22mm elbows
`
at 0.8m each = 3.2m
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
`
equates to: 14m
As the actual length is 7m, a 28mm (D2) copper
`
pipe will be satisfactory.
Safety device
(e.g. temperature
relief valve)
Metal discharge pipe (D1) from
temperature relief valve to tundish
600mm
maximum
300mm
maximum
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulations G3 section 3.56,
Table 4 and worked example
Figure/Table 5
Valve outlet size
G1/2
1.4m
G1
10
maximum
permitted
Discharge below
Tundish
fixed grating
(Building
Regulation G3
section 3.61
gives alternative
points of
discharge
Fixed grating
Trapped gully
Minimum size of
discharge pipe D1
15mm
22mm
28mm
length
Minimum size of
Maximum resistance
discharge pipe D2
allowed, expressed
from tundish
as a length of straight
pipe (ie no elbows or
22mm
28mm
35mm
28mm
35mm
42mm
35mm
42mm
54mm
Resistance created
by each elbow 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
bend
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.3m
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