Potterton Promax Store 24 Installation And Service Manual page 19

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 takes 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 G1/2 temperature
relief valve with a discharge pipe (D2) having 4
No. 28mm 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
G1/2 temperature relief valve is 9.0 m.
Subtract the resistance for 4 No. 22 mm elbows
at 0.8m 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 28 mm pipe (D2) from a G1/2 temperature
relief valves equates to 18 m.
Subtract the resistance of 4 No. 28 mm elbows
at 1.0 m each - 4.0 m.
Therefore the maximum permitted length
equates to: 14 m.
As the actual length is 7 m, a 28 mm min. (D2)
copper pipe will be satisfactory.
Warnings
• Under No circumstances should the factory
fitted Temperature/Pressure Relief Valve be
removed other than by Authorised Potterton
personnel. To do so will invalidate any
warranty or claim.
• The cold water Inlet Control Group must be
fitted to the mains water supply to the
Promax Store when it is operated as an
unvented system.
• Control and safety valves MUST NOT be
tampered with.
• The discharge pipe MUST NOT be blocked
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
Valve Minimum Minimum
outlet discharge discharge
size pipe D1 pipe D2
from
tundish
22 mm
G1/2 15 mm 28 mm
35 mm
28 mm
G3/4 22 mm 35 mm
42 mm
35 mm
G1 28 mm 42 mm
54 mm
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.
Typical Discharge Pipe Arrangement
Safety device
(e.g. Temperature
Metal discharge pipe (D1) from
relief valve)
Temperature relief valve to tundish
600mm maximum
300mm
minimum
Discharge pipe (D2 from tundish,
with continuous fall. See Building
Regulation G3 section 3.56,
Table 4 and worked example)
Maximum Resistance
resistance created by
allowed, each elbow
expressed or bend
as a length
of straight
pipe (i.e. no
elbows or
bends)
up to 9 m 0.8 m
up to 18 m 1.0 m
up to 27 m 1.4 m
up to 9 m 1.0 m
up to 18 m 1.4 m
up to 27 m 1.7 m
up to 9 m 1.4 m
up to 18 m 1.7 m
up to 27 m 2.4 m
Tundish
Discharge below
fixed grating
(Building Regulation
G3 section 3.61 gives
alternative points
of discharge)
Fixed grating
Trapped
gully
Fig. 8
19