Heatrae Sadia ELECTROMAX Installation & Servicing Instructions Manual page 16

3.53 Where valves
temperature and pressure relief valve from a
single unvented hot water system 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
3.54 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 600mm of pipe between the valve
outlet and the tundish (diagram 11 & Table 1,
page 18).
Note: To comply with the Water Supply (Water
Fittings) Regulations, the tundish should
incorporate a suitable air gap.
3.55 Any discharge should be visible at the
tundish. In addition, where discharges from
safety devices may not be apparent, e.g. in
dwellings occupied by people with impaired
vision or mobility, consideration should be
given to the installation of a suitable safety
device to warn when discharge takes place,
e.g. electronically operated.
Discharge pipe D2 (not supplied)
3.56 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 (see diagram
1, G3), (diagram 11, page 18); and
(b) be installed with a continuous fall
thereafter of at least 1 in 200.
3.57 The discharge pipe (D2) should be
made of:
(a) metal; or
(b) other material that has been demonstrated
to be capable
temperatures of the water discharged and is
clearly and permanently marked to identify
16 Installation & Servicing Instructions
other than
of safely withstanding
the the product and performance standard (e.g.
as specified in the relevant part of BS 7291).
3.58 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 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.
(See diagram 1, Table 1, G3), (diagram 11 &
Table 1, page 18 in these instructions) and the
worked example.
Note: An alternative approach for sizing
discharge pipes would be to follow Annex D,
section D.2 of BS 6700:2006 Specification for
design, installation, testing and maintenance
of services supplying water for domestic use
within buildings and their curtilages.
3.59 Where a single common discharge
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 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