Unvented Hot Water Cylinder
- 20-
4.3.1
Building Regulation G3
The following text is reproduced from the Building Regulations.
It is included here for reference only.
Discharge pipes from safety devices
Discharge pipe D1
3.49 Each of the temperature relief valves or combined temperature and valves specified should discharge either directly
or by way of a manifold via a short length of metal pipe (D1) to a tundish.
3.50 The diameter of discharge pipe (D1) should be not less than the nominal outlet size of the temperature relief valve.
3.51 Where a manifold is used it should be sized to accept and discharge the total discharge from the discharge pipes
connected to it.
3.52 Where valves other than the temperature and pressure relief valve from a single unvented discharge by way of the
same manifold that is used by the safety devices, the manifold should be factory fitted as part of the hot water storage
system unit or package.
Tundish
3.53 The tundish should be vertical, located in the same space as the unvented hot water storage system and be fitted as
close as possible to, and lower than, the valve, with no more than 750mm of pipe between the valve outlet and the tundish
(see Diagram1).
Note: To comply with the Water Supply (Water Fittings) Regulations, the tundish should incorporate a suitable air gap.
3.54 Any discharge should be visible at the tundish. In addition, where discharges from safety devices may not be apparent,
e.g. in dwelling occupied by people with impaired vision or mobility, consideration should be given to the installation of a
suitable safety device to warm when discharge takes place, e.g. electronically operated.
Discharge pipe D2
3.55 The discharge pipe (D2) from the tundish should:
a.
Have a vertical section of pipe at least 300mm long below the tundish before any elbows or bends in pipework (see
Diagram 1); and
b.
Be installed with a continuous fall thereafter of least 1 in 200.
3.56 The discharge pipe (D2) should be made of:
a.
Metal; or
b.
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 (e.g. as
specified in the relevant part of BS 7291).
3.57 The discharge pipe D2 should 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. for discharge pipes between 9m and 18m
the equivalent resistance length beat least two sizes larger than the nominal outlet size of the safety device; between 18m
and 27m at least 3 sizes larger, and so on; bends must be taken into account in calculating the flow resistance. See diagram
1, table 1 and worked example.
Note: an alternative approach for sizing discharge pipes would be to allow Annex D, section D.2 of BS 6700:2006
Specification for design, installation, testing and maintenance of devices supplying water for domestic use within buildings
and their curtilages.
