8
Discharge
- Building Regulations:
Discharge pipes must be installed in accordance with the latest edition of the Building Regulations.
Discharge Pipes
The discharge pipe (D1) from the vessel up to and including the tundish is generally supplied by
the manufacturer of the hot water storage system (see paragraph 3.5). Where otherwise, the
installation should include the discharge pipe(s) (D1) from the safety device(s). In either case the
tundish should be vertical, located in the same space as the unvented hot water storage system
and be fitted as close as possible and within 500mm of the safety device e.g. the temperature relief
valve.
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, be of metal and:
a.
be at least one pipe size larger than the normal outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of a straight pipe 9m long i.e. discharge pipes
between 9m and 18m 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. Refer to Diagram 1, Table
1 and the worked example. An alternative approach for sizing discharge pipes would be to
follow BS 6700: 1987
Specification for design installation, testing and maintenance of
services supplying water for domestic use within buildings and their curtilages, Appendix E,
section E2 and table 21.
b.
have a vertical section of pipe at least 300mm long, below the tundish before any elbows or
bends in the pipework.
c.
be installed with a continuous fall.
d.
have discharges visible at both the tundish and the final point of discharge but where this is not
possible or is practically difficult there should be clear visibility at one or other of these
locations. Examples of acceptable discharge arrangements are:
i.
ideally below a fixed grating and above the water seal in a trapped gully.
ii.
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 where children may play or
otherwise come into contact with discharges a wire cage or similar guard is positioned to
prevent contact, whilst maintaining visibility.
iii.
discharges at high level; e.g. into a metal hopper and metal down pipe with the end of the
discharge pipe clearly visible (tundish visible or not) or onto a roof capable of withstanding high
temperature discharges of water and 3 m from any plastics guttering system that would
collect such discharges (tundish visible).
iv.
where a single pipe serves a number of discharges, such as in blocks of flats, the number served
should be limited to not more than 6 systems so that any installation discharging can be traced
reasonably easily. The single common discharge pipe should be at least one pipe size larger
than the largest individual discharge pipe (D2) to be connected. If unvented hot water storage
systems are installed where discharges from safety devices may not beapparent 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.
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