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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 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 instalation 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 be apparent 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.
Worked example of discharge pipe sizing
The example below is for a G1/2 temperature relief valve with a discharge pipe (D2) having
4 No. elbows and length of 7m from the tundish to the point of discharge.
From Table 1:
Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2)
from a G1/2 temperature relief valve is 9.0m.
Subtract the resistance for 4 No. 22mm elbows at 0.8m each = 3.2m
Therefore the permitted length equates to: 5.8m
5.8m is less than the actual length of 7m therefore calculate the next largest size.
Maximum resistance allowed for a straight length of 28mm pipe (D2) from a G1/2 tempera-
ture relief valve equates to 18m.
Subtract the resistance of 4 No. 28mm elbows at 1.0m each = 4.0m
Therefore the maximum permitted length equates to: 14m
As the actual length is 7m, a 28mm (D2) copper pipe will be satisfactory.
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