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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 fittings 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 fixed grating and above the water seal;
(b) downward discharges at low level; i.e. up to
100 mm 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 down pipe with the end of the discharge pipe
clearly visible or onto a roof capable of withstanding
high temperature discharges of water and 3 m from
any plastic guttering system that would collect such
discharges.
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. 4: shows a G1/2 temperature relief valve with a
discharge pipe (D2) having 4 No. elbows and length of
7 m from the tundish to the point of discharge.
From Table 4, page 10:
Maximum resistance allowed for a straight length of 22
mm copper discharge pipe (D2) from a G1/2
temperature relief valve is 9 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
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 m each = 4 m
Therefore the maximum permitted length equates to:
14 m
As the actual length is 7 m, a 28 mm (D2) copper pipe
will be satisfactory.
Warnings:
•
Under no circumstances should the factory fitted
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 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.
9
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