Jet 120i, Installation & Servicing Instructions Manual, Page: 9 / 24

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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
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, roofing felt and non-
metallic rainwater goods may be damaged by such
discharges.
Worked Example of Discharge Pipe Sizing
Fig. 04: 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 03:
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 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.