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INSTALLATION INSTRUCTIONS
The two safety valves will only discharge water under fault conditions. When
operating normally water will not be discharged. The tundish should be located in
the same space as the unvented hot water storage system and be fitted as close as
possible to, and lower than, the safety device, with no more than 600mm of pipe
between the valve outlet and the tundish. The tundish should be positioned away from
electrical devices.
The tundish should be located in a position so that any discharge is visible.
In addition, where discharges from safety devices may not be apparent, extra
consideration should be given, e.g. for people with impaired vision or mobility. This
could be via the installation of a suitable electronically operated or other safety
device to warn when discharge takes place.
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 the pipework.
B) Be installed with a continuous fall of at least 1 in 200 thereafter.
The discharge pipe (D2) from the tundish should be of metal or other material that
has been demonstrated to be capable of withstanding temperatures of the water
discharged.
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. Therefore, 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 three sizes larger. Bends
must be taken into account in calculating the flow resistance. Refer to the diagram,
Table 2 and the worked example.
An alternative approach for sizing discharge pipes would be to follow BS EN 806:2
specifications for design, installation, testing and maintenance of services supplying
water for domestic use within buildings and their curtilages.
The discharge pipe (D2) should terminate in a safe place where there is no risk
to persons in the vicinity of the discharge. Examples of acceptable discharge
arrangements are:
(CONTINUED)
A) To a trapped gully with the end of the pipe below the fixed grating and above the
water seal.
B) 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 could come into contact with discharges – a visible
wire cage or similar guard is positioned to prevent contact.
C) Discharges at a high level; e.g. into a metal hopper and metal down pipe with
the end of the discharge pipe clearly visible; or onto a roof capable of withstanding
high temperature discharges of water and 3m from any plastic guttering systems that
would collect such discharges.
D) Device to warn when discharge takes place.
Discharge worked example
The example below is for G1/2 temperature relief valve with a discharge pipe (D2)
having four elbows and a length of 7m from the tundish to the point of discharge.
Maximum resistance allowed for a straight length of 22mm copper discharge pipe
(D2) from a G1/2 temperature relief valve is: 9.0m.
Subtract the resistance for four 22mm elbows at 0.8m each = 3.2m.
Therefore the maximum permitted length equates to: 5.8m.
5.8m is less than the actual length of 7m, therefore calculate the next largest size.
Maximum resistance allowed for a straight length of 28mm pipe (D2) from a G1/2
temperature relief valve equates to: 14m.
As the actual length is 7m, a 28mm (D2) copper pipe will be satisfactory.
Table 2: Sizing of copper discharge pipe 'D2' for a temperature relief valve with a
G1/2 outlet size (as supplied).
Size of
Maximum length of
discharge
straight pipe
pipework
(no bends or elbows)
22mm
Up to 9m
28mm
Up to 18m
35mm
Up to 27m
Green Storage WB Range
Installation & Maintenance Instructions
Deduct the figure below from the
maximum length for each bend or
elbow in the discharge pipe
0.8m
1.0m
1.4m
7
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