Heatrae Sadia Multipoint 30H, Fitting Instructions Manual

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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 maximum permitted length
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
Tundish
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulations G3 section 3.56,
Table 4 and worked example
Discharge below
fixed grating
(Building
Regulation G3
section 3.61
gives alternative
points of
discharge
Fixed grating
Trapped gully
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 (ie 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
1.4m 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
Figure/Table 5