Technical data

13
GEMINI HSC
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
9 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 Table 1 and the worked example on page 14.
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.
10.2 terminating safety discharge pipes (contd)