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Tundish
3.54 – The tundish should be vertical, located
`
in the same space as the unvented hot water
storage system and be fitted as close as possible
to, and lower than, the valve, with no more than
600mm of pipe between the valve outlet and the
tundish (see fig 15).
Note:
To comply with the Water Supply (Water Fittings)
`
Regulations, the tundish should incorporate a
suitable air gap.
3.55 – Any discharge should be visible at the
`
tundish.
In addition, where discharges from
safety devices may not be apparent, e.g. in
dwellings occupied by people with impaired
vision or mobility, consideration should be
given to the installation of a suitable safety
device to warn when discharge takes place, e.g.
electronically operated.
Discharge pipe D2
3.56 – The discharge pipe (D2) from the tundish
`
should:
• (a) have a vertical section of pipe at least
300mm long below the tundish before any
elbows or bends in the pipework (see fig. 15);
and
• (b) be installed with a continuous fall
thereafter of at least 1 in 200.
3.57 – The discharge pipe (D2) should be made
`
of:
• (a) metal; or
• (b) other material that has been demonstrated
to
be
capable
temperatures of the water discharged and is
clearly and permanently marked to identify
the product and performance standard (e.g.
as specified in the relevant part of BS 7291).
3.58 – The discharge pipe (D2) should be at
`
least one pipe size larger than the nominal
outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of
a straight pipe 9m long, i.e. for discharge pipes
between 9m and 18m the equivalent resistance
length should be at least two sizes larger than
the nominal outlet size of the safety device;
between 18 and 27m at least 3 sizes larger,
and so on; bends must be taken into account
in calculating the flow resistance. See figure 5,
table 5 and the worked example.
Note:
An alternative approach for sizing discharge
`
pipes would be to follow Annex D, section D.2
of BS 6700:2006 Specification for design,
installation, testing and maintenance of services
supplying water for domestic use within buildings
and their curtilages.
of
safely
withstanding
3.59 – Where a single common discharge pipe
`
serves more than one system, it should be
at least one pipe size larger than the largest
individual discharge pipe (D2) to be connected.
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
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 polybutylene (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.
a
mechanical
seal,
not
9
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