8
3.60 The discharge pipe should not be connected to
a soil discharge stack unless it can be demonstrated
that the soil discharge stack is capable of safely
withstanding temperatures of the water discharged,
in which case, it should:
(a) contain a mechanical seal, not incorporating
a water trap, which allows water into the branch
pipe without allowing foul air from the drain to be
ventilated through the tundish;
(b) be a separate branch pipe with no sanitary
appliances connected to it;
(c) if plastic pipes are used as branch pipes
carrying discharge from a safety device they should
be either polybutalene (PB) to Class S of BS 7291-
2:2006 or cross linked polyethylene (PE-X) to Class
S of BS 7291-3:2006; and
(d) be continuously marked with a warning that no
sanitary appliances should be connected to the pipe.
Note:
1. Plastic pipes should be joined and assembled
with ttings appropriate to the circumstances in which
they are used as set out in BS EN ISO 1043-1.
2. Where pipes cannot be connected to the
stack it may be possible to route a dedicated pipe
alongside or in close proximity to the discharge stack.
Termination of discharge pipe
3.61 The discharge pipe (D2) from the tundish
should terminate in a safe place where there is no
risk to persons in the vicinity of the discharge.
3.62 Examples of acceptable discharge
arrangements are:
(a) to a trapped gully with the end of the pipe below
a xed grating and above the water seal;
(b) downward discharges at low level; i.e. up to
100mm above external surfaces such as car parks,
hard standings, grassed areas etc. are acceptable
providing that a wire cage or similar guard is
positioned to prevent contact, whilst maintaining
visibility; and
(c) discharges at high level: e.g. into a metal
hopper and metal downpipe with the end of the
discharge pipe clearly visible or onto a roof capable
of withstanding high temperature discharges of
water and 3m from any plastic guttering system that
would collect such discharges.
3.63 The discharge would consist of high
temperature water and steam. Asphalt, roong felt
and non-metallic rainwater goods may be damaged
by such discharges.
Worked example of discharge pipe sizing
Fig. 5: 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 3:
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.
WARNINGS:
• Under no circumstances should the factory tted
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 tted on the mains water supply to the cylinder.
• No control or safety valves should be tampered with
or used for any other purpose.
• The discharge pipe should not be blocked or used
for any other purpose.
• The tundish should not be located adjacent to any
electrical components.
