15
TUDOR NHRE
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 (eg. the temperature relief valve)
and must be away from any electrical device.
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 nominal outlet size of the safety device unless its total
equivalent hydraulic resistance exceeds that of a straight pipe 9m long ie: 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 18m 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 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 trapped gully.
ii.
downward discharges at low level, ie: up to 100mm above external surfaces such as car parks,
hard standings, grassed areas etc. are acceptable providing that where children may play and
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; eg: 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 3m 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 last individual discharge pipe (D2) to be connected. If unvented hot water storage systems
are installed where discharges from safety devices may not be apparent ie: 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 rain water goods may be damaged by such discharges. Where children may
play or otherwise come in contact with discharges, a wire cage or similar guard must be
positioned to prevent contact whilst maintaining visibility.
• Maximum resistance allowed fro a straight length of 35mm pipe (D2) from G 3/4 T&P valve
equates to: 18m.
• Subtract the resistance for 4 no. 35mm elbow at 1.4 each = 5.6m.
• Therefore the maximum permitted length equates to: 14.4m
• As the actual length is 7m, a 35mm (D2) copper pipe will be satisfactory.
Содержание TUDOR NHRE 18
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