6
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.
WARNINGS
• Under no circumstances should the factory fit-
ted temperature/pressure relief valve be removed
other than by a competent person. To do so will
invalidate any guarantee or claim.
• The cold water combination valve assembly must
be fitted to the mains water supply to the Pullin
Evolution Solar unit.
• No control or safety valves should be tampered
with.
• The discharge pipe should not be blocked or
used for any other purpose.
• The tundish should not be located adjacent to
any electrical components.
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 2: Sizing of copper discharge pipe (D2) for common temperature relief valve outlet sizes
Fixed grating
Discharge below
fixed grating
(Building Regulation
G3 section 3.9d gives
alternative points
of discharge)
Trapped
gully
Discharge pipe (D2) from tundish,
with continuous fall. See Building
Regulation G3 section 3.9d i-iv,
Table 4 and worked example
300mm
minimum
500mm maximum
Metal discharge pipe (D1) from
Temperature relief valve to tundish
Tundish
Safety device
(e.g. Temperature
relief valve)
Fig.4: Typical discharge pipe arrangement (extract from Building Regulation G3 Guidance section)