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Discharge Arrangement
Discharge Pipework
The inlet control group should be positioned so that the discharge from both safety valves can be
combined via a 15mm end feed tee. Connect the tundish and route the discharge pipe which must
be routed in accordance with Building Regulations - 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, and lower than the
valve, with no more than 600mm between the safety device outlet e.g. the temperature relief valve
and the tundish.
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:
•
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.
•
Have a vertical section of pipe at least 300mm long, below the tundish before any elbows or
bends in the pipework.
•
Be installed with a continuous fall.
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.
Boss Direct / Indirect Installation Guide
35
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