Heatrae Sadia ELECTROMAX Installation & Servicing Instructions Manual page 16

Water may drip from the discharge pipe of
the pressure-relief device and that this pipe
must be left open to the atmosphere.
The pressure-relief device is to be operated
regularly to remove lime deposits and to
verify that it is not blocked.
The discharge pipe connected to the
pressure relief device is to be installed in a
continuously downward direction and in a
frost free environment
G3 GUIDANCE SECTION 3.9
The discharge pipe (D1) (see Diagram
11, page 17) from the vessel up to and
including the tundish is generally supplied
by the manufacturer of the hot water storage
system. Where otherwise, the installation
should include the discharge pipe(s) (D1)
from the safety device(s). In either case
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, preferably 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 two
pipe sizes larger, and so on. Bends must
be taken into account in calculating the flow
resistance. Refer to Diagram 11, Table 1 and
the worked example.
An alternative approach for sizing discharge
pipes would be to follow BS6700:1987
Specification for design, installation, testing
and maintenance of services supplying water
for domestic use within buildings and their
cartilages, Appendix E, section E2 and Table
21.
16 Installation & Servicing Instructions
b. have a vertical section of pipe at least
300mm long below the tundish before any
elbows or bends in the pipework.
c. be installed with a continuous fall.
d. have discharges visible at both the tundish
and final point of discharge, but where this
is not possible or is practically difficult there
should be clear visibility at one or other of
these locations.
E x a m p l e s o f a c c e p t a b l e d i s c h a r g e
arrangements are:
i. ideally below a fixed grating and above
the water seal in a trapped gully.
ii. Downward discharges at 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 may play or otherwise come into
contact with discharges a wire cage or similar
guard is positioned to prevent contact, whilst
maintaining visibility.
iii. Discharges at high level; e.g. into
a 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 plastics guttering
system that would collect such discharges
(tundish visible).
iv. 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
discharging can be traced reasonably easily.
The single common discharge pipe should
be at least one pipe size larger than the
largest individual discharge pipe (D2) 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, consideration should be given to
the installation of an electronically operated
device to warn when discharge takes place.
Note: The discharge will consist of scalding
water and steam. Asphalt, roofing felt and non-
metallic rainwater goods may be damaged by
such discharges.