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DISCHARGE ARRANGEMENT
Note: It is not acceptable to discharge straight into a soil pipe
Note: The discharge will consist of scalding water and steam. Asphalt, roofing felt and non‐metallic rainwater goods may be damaged by such
discharges.
The inlet control group should be positioned so that the discharge from both safety valves can be combined via a 15mm end
feed Tee, as in the diagram above.
Connect the tundish and route the discharge pipe which must be routed in accordance with Building regulation ‐ Part G3 of
schedule 1.
When operating normally water will not be discharged. Water discharge from the two safety valves will only occur under fault
conditions.
The tundish should be vertical, located in the same space as the unvented hot water storage system and be fitted as close as
possible, within 500mm of the safety device e.g. the temperature relief valve.
The position of the tundish must be that when installed it is visible to the occupants of the premises.
When positioning the tundish, the drain valves and motorised valve ensure that these items are positioned away from any
electrical devices.
The discharge pipe (D2) coming 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, 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 BS6700
Specification for design, installation, testing and maintenance of services supplying water for domestic use within
buildings and their curtilages.
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) It is preferable for the discharge to be visible at both the tundish and the final point of discharge. Where this is not
possible or practically difficult, there should be clear visibility at one or other of these locations.
Examples of acceptable discharge arrangements are:
1. Ideally below the fixed grating and above the water seal in a trapped gulley.
2. Downward discharges at a 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 play or otherwise come into contact with discharges, a wire cage or similar guard is positioned to
prevent contact whilst maintaining visibility.
3. Discharges at a high level; e.g. in to metal hopper and metal down pipe with the end of the discharge pipe clearly visible (tundish visible or
unvented hot water cylinders
installation and maintenance instructions
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