12
INSTALLATION
qSpa -
Installation and Servicing
15 mm
discharge
pipe
Expansion
relief valve
Typical Discharge Pipe Arrangement
Dotted line showing
alternative route with
single tundish being used
500 mm max.
P & T
Relief
Valve
300 mm
min.
22 mm metal pipe with continuous
fall up to 9m equivalent length (D2).
NOTES
:
The discharge will consist of scalding
waterand steam. Asphalt, roofing felt
and non-metallic rainwater goods may
be damaged by such discharges.
It is not acceptable to discharge straight
into a soil pipe.
Discharge below
fixed grating
Fixed Grating
Trapped gully
The relief valve should be installed to
discharge in accordance with G3 of
the Approved Document of the Building
Regulations and should be piped to where it
is visible, but will not cause danger to persons
or damage to materials.
The following information is taken from
Approved Document G3 of the Building
Regulations and is provided to assist with
the design and installation of the discharge
pipework. However, the information is not
exhaustive and reference should always
be made to Approved Document G3 of the
Building Regulations. The final decision
regarding any arrangements rests with
Building Control and it is recommended
that their advice is sought if you have
any concerns regarding this aspect of the
installation.
The two safety valves will only discharge
water under fault conditions. When operating
normally water will not be discharged.
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 within 500mm of the safety
device e.g. the temperature relief valve.
The discharge pipe (D2) 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:
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. Refer to the table 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.
b) Have a vertical section of pipe at least
300mm long, below the tundish before
any elbows or bends in the pipe work.
c) Be installed with a continuous fall.
Worked Example
The example below is for G1/2 temperature relief valve with a discharge
pipe (D2) having 4 elbows and length of 7m from the tundish to the point of
discharge.
From the table below:
Maximum resistance allowed for a straight length of 22mm copper discharge
pipe (D2) from a G1/2 temperature relief valve is: 9m subtract the resistance
for 4 x 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.
Sizing of copper discharge pipe ‘D2’ for a temperature relief valve
with a G1/2 outlet size (as supplied)
Size of discharge
pipework
Maximum length of
straight pipe
(no bends or elbows)
Deduct the figure
below from the
maximum length for
each bend or elbow in
the discharge pipe
22mm
Up to 9m
0.8m
28mm
Up to 18m
1m
35mm
Up to 27m
1.4m
PRESSURE & TEMPERATURE/EXPANSION RELIEF VALVE PIPEWORK
continued . . . . .
INST
ALLA
TION
