UK Manufactured Unvented Hot Water Cylinder Installation Guide
47
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 accord-
ance 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 equiva-
lent 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.
