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6.3.2
RECOMMENDED PIPEWORK FOR A STORAGE APPLIANCE
6.3.3
TEMPERATURE AND PRESSURE RELIEF VALVE
A temperature and pressure relief valve is provided in the unvented water system kit. This valve has a lift pressure of 7
bar and a lift temperature of 90°C. The valve must be fitted to the relief valve tapping.
The storage vessel relief valve connection should not be used for any other purpose.
6.3.4
RELIEF VALVE DISCHARGE PIPEWORK
It is important that any discharge water does not collect in the discharge pipe-work and can run freely to the tundish. The
tundish should be mounted in a vertical and visible position located in the same space as the unvented hot water storage
system and be fitted as close as possible and within 600mm of the safety device e.g. the temperature relief valve.
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 or other material that has been demonstrated to be capable of safely withstanding
temperatures of the water discharged and is clearly and permanently marked to identify the product and performance
standard, 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.
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 of at least 1 in 200.
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