1
9
Fig.
8
Valve
M
inimum
M
inimum
M
aximum Resistance
outlet discharge discharge resistance created by
size pipe D1 pipe D2 allowed, each elbow
from expressed or bend
tundish as a length
of straight
pipe (i.e. no
elbows or
bends)
22 mm up to 9 m 0.
8
m
G
1
/2
15
mm 2
8
mm up to
18
m
1
.0 m
3
5
mm up to 2
7
m
1
.4 m
2
8
mm up to 9 m
1
.0 m
G3/4 22 mm 3
5
mm up to
18
m
1
.4 m
42 mm up to 2
7
m
1
.
7
m
3
5
mm up to 9 m
1
.4 m
G
1
2
8
mm 42 mm up to
18
m
1
.
7
m
5
4 mm up to 2
7
m 2.4 m
Table
1
. Sizing of copper discharge pipe (D2) for common temperature
relief valve outlet sizes.
Note:
shaded area is reproduced for
completeness but does not apply to this boiler.
may not be apparent i.e. in
dwellings
occupied by blind, infirm or disabled
people, consideration should be given to
the installation of an electronically operated
device to warn when discharge ta
k
es place.
Note:
The discharge will consist of scalding
water and steam. Asphalt, roofing felt and
non-metallic rainwater goods may be
damaged by such discharges.
Worked example of discharge pipe sizing
The example below is for a G
1
/2 temperature
relief valve with a discharge pipe (D2) having 4
No. 2
8
mm elbows and length of
7
m from the
tundish to the point of discharge.
From Table
1
:
Maximum resistance allowed for a straight length
of 22mm copper discharge pipe (D2) from a
G
1
/2 temperature relief valve is 9.0 m.
Subtract the resistance for 4 No. 22 mm elbows
at 0.
8
m each = 3.2 m.
Therefore the permitted length equates to:
5
.
8
m.
5
.
8
m is less than the actual length of
7
m
therefore calculate the next largest size.
Maximum resistance allowed for a straight length
of 2
8
mm pipe (D2) from a G
1
/2 temperature
relief valves equates to
18
m.
Subtract the resistance of 4 No. 2
8
mm elbows
at
1
.0 m each - 4.0 m.
Therefore the maximum permitted length
equates to:
1
4 m.
As the actual length is
7
m, a 2
8
mm min. (D2)
copper pipe will be satisfactory.
Warnings
• Under No circumstances should the factory
fitted Temperature/
P
ressure Relief Valve be
removed other than by Authorised
P
otterton
personnel. To do so will invalidate any
warranty or claim.
• The cold water Inlet
C
ontrol Group must be
fitted to the mains water supply to the
P
romax Store when it is operated as an
unvented system.
•
C
ontrol and safety valves MUST NOT be
tampered with.
• The discharge pipe MUST NOT be bloc
k
ed
or used for any other purpose.
• The tundish must not be removed but can be
sited outside the RH panel using the opening
provided.
• Electrical components must not be sited near
the tundish.
© Baxi Heating UK Ltd 2015
300mm
minimum
Safety
device
(e.g.
Temperature
re
l
ief
va
l
ve)
Meta
l
discharge
pipe
(D
1
)
from
Temperature
re
l
ief
va
l
ve
to
tundish
Tundish
Discharge
be
l
ow
fi
x
ed
grating
(Bui
l
ding
Regu
l
ation
G3
section
3.6
1
gives
a
l
ternative
points
of
discharge)
Fi
x
ed
grating
Trapped
gu
ll
y
Discharge
pipe
(D2
from
tundish,
with
continuous
fa
ll
.
See
Bui
l
ding
Regu
l
ation
G3
section
3.
5
6,
Tab
l
e
4
and
wor
k
ed
e
x
amp
l
e)
600mm
ma
x
imum
Typical Discharge
P
ipe Arrangement