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4.9. Discharge arrangement.
The tundish must be installed in a position so that it is clearly visible by the user. In addition,
the discharge pipe 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
equipment hydraulic resistance exceeds that of a straight pipe 9 m long, i.e. discharge pipes
between 9 m and 18 m equivalent resistance length should be at least two sizes larger then the
normal outlet size of the safety device, between 18 m and 27 m at least three sizes larger and so
on. Bends must be taken into account in calculating the flow resistance. Refer to the diagram,
tables and worked example detailed below.
(b) Have a vertical section of pipe at least 300 mm 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 Tundish and the final point of discharge, but where this is not
possible or practically difficult, examples of acceptable discharge arrangements are:
•
Ideally below a fixed grating and above the water seal in a trapped gully
•
Downward discharge at low level, i.e. up to 100 mm above external surfaces such as car
parks, hard standings, grassed areas, etc. are acceptable providing that where children play or
otherwise come into contact with discharges, a wire cage or similar guard is positioned to prevent
contact whilst maintaining visibility.
•
Discharge 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 plastic guttering system that would collect
such discharges (Tundish visible).
•
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 six 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 to be
connected. If unvented hot water storage
systems are installed where discharges
from safety devices may not be apparent
i.e. in dwellings occupied by blind, or
disabled people, consideration should be
given to the installation of an electrically
operated device to warn when discharge
takes place.
Warning Notice
– The discharge will
consist of scalding water and steam.
Asphalt, roofing felt and non-metallic
rainwater goods may be damaged by
Figure 3 - Typical discharge pipe arrangement.
TUNDISH
SAFETY
DEVICE
500mm MIN
300mm MIN
Metal discharge pipe from
temperature relief valve to tundish
Safety device (Eg: Temp relief valve)
Discharge below fixed grating
Fixed Grating
Trapped Gullley
Metal discharge pipe from Tundish
with continuous fall.
