Oversink and Undersink Water Heater
- 12-
Worked Example
The example below is for a G ½
temperature relief valve
with discharge pipe (D2) having 4 No. 22mm elbows and length
of 7m from the
tundish
to the point of discharge.
From Table1
Maximum resistance allowed for a straight length of 22mm copper discharge pipe (D2) from a G ½ t
emperature relief
valves
is: 9.0m
Subtract the resistance for 4 No.22mm elbows at 0.8m each=3.2m
Therefore the maximum permitted length equates to: 5.8m which is less than the length of 7m therefore calculated the
next largest size.
Maximum resistance allowed for a straight length of 28mm copper discharge pipe (D2) from a G ½
temperature relief
valve
is. 18m
Subtract the resistance for 4 No.28mm elbows at 1.0m each=4m
Therefore the maximum permitted length equates to: 14m
As the actual length is 7m, a 28mm (D2) copper pipe will be satisfactory.
3.59
Where a single common discharged pipe serves more than one system, it should be at least one pipe size larger than
the largest individual discharge pipe (D2) to be connected.
3.60
The discharge pipe should not be connected to a soil discharge stack unless it can be demonstrated that the soil
discharge stack is capable of safely withstanding temperatures of the water discharged, in which case, it should:
a.
Contain a mechanical seal, not incorporating a water trap, which allows water into the branch pipe without
allowing foul air from the drain to be ventilated through the
tundish
;
b.
Be a separate branch pipe with no
sanitary appliances
connected to it;
c.
If plastic pipes are used as branch pipes carrying discharge from a safety device they should be either
polybutalene (PB) to Class S of BS 7291-2:2006 or cross linked polyethylene (PE-X) to Class S of BS 7291-3:2006;and
d.
Be continuously marked with a warning that no
sanitary appliance
should be connected to the pipe.
Notes
:
1.
Plastic pipes should be joined and assembled with fittings appropriate to the circumstances in which they are
used as set out in BS EN ISO 1043-1:2002
Plastics: Symbols and abbreviated terms. Basic polymers and their special
characteristic
.
2.
Where pipes cannot be connected to the stack it may be possible to route a dedicated pipe alongside or in close
proximity to the discharge stack.
Termination of discharge pipe
3.61
Discharge pipe D2 from
tundish
should terminate in safe place where there is no risk to persons in vicinity of
discharge.
3.62
Examples of acceptable discharge arrangements are:
a.
To a trapped gully with the end of the pipe below a fixed grating and above the water seal;
b.
Downward discharge at low level; i.e. up to 100mm above external surfaces such as a car parks, hard standings,
grassed areas etc. are acceptable providing that a wire cage or similar guard is positioned to prevent contact,
whilst maintaining visibility; and,
c.
Discharge at high level: e.g. into metal hopper and metal downpipe with the end of the discharge pipe clearly
visible or onto a roof capable of withstanding high temperature discharges of water and 3 m to any plastic
guttering system that would collect such discharges.
3.63
The discharge would consist of high temperature water and steam. Asphalt, roofing felt and non-metallic rainwater
goods may be damage by such discharges.
WARNING: If the discharge from the tundish D2 is connected to a soil stack, then the soil stack should be
manufactured of a material which can accommodate temperatures of excess of 95C .
Discharge pipe D2 is allowed under the new Buildings Regulations G3 to be of a material other than metal. When
plastic pipes are used these should be certified to a standard which proves that the pipes are acceptable for use at
temperatures in excess of 100C.
