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Examples Of Acceptable Dischargement Arrangements
Ideally below the fixed grating and above the water seal in a trapped gulley.
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 come into
contact with discharges, a wire cage or similar guard is positioned to prevent contact whilst maintaining
visibility.
Discharges at a high level
; e.g. in to metal hopper and metal down pipe with the end of the discharge pipe
clearly visible (tundish visible or not) or onto a roof capable of withstanding high temperature discharges
of water and 3m from any plastic guttering systems that would collect such discharges (tundish available).
Where a single pipe serves a number of discharges, such as in blocks of flats, the number served should be limited
to not more than 6 systems so that any installation can be traced reasonably easily.
The single common discharge pipe should be at least one pipe size larger than the largest individual dis-
charge pipe to be connected. If unvented hot water storage systems are installed where discharges from
safety devices may not be apparent, i.e. in dwellings occupied by blind, infirm or disabled people, con-
sideration should be given to the installation of an electronically operated device to warn when discharge
takes place.
Worked Example
The example on the next page is for G1/2 temperature relief valve with a discharge pipe (D2) having 4 No.
elbows and 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 tem-
perature relief valve is: 9.0m. Subtract the resistance for 4 No. 22mm elbows at 0.8m each = 3.2m. There-
fore 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.
G 1/2
G 3/4
G1
Min. size of discharge pipe D1
15mm
22mm
28mm
Min. size of discharge pipework
D2 from tundish
22mm 28mm 35mm 28mm 35mm 42mm 35mm 42mm 54mm
Max. length of straight pipe (no
bends or elbows)
Up to
9m
Up to
18m
Up to
27m
Up to
9m
Up to
18m
Up to
27m
Up to
9m
Up to
18m
Up to
27m
Deduct the figure below from the
maximum length for each bend or
elbow in the discharge pipe
0.8m
1.0m
1.4m
1.0m
1.4m
1.7m
1.4m
1.7m
2.3m
Sizing of copper discharge pipe (D2) for a temp. relief valve with a G1/2 outlet size (as supplied)
Discharge Arrangement
