Benchmark Centerstore 120 Installation And Servicing Instructions page 6

DISCHARGE PIPEWORK
It is a requirement of Building Regulation G3
that any discharge from an unvented system is
conveyed to where it is visible, but will not cause
danger to persons in or about the building. The
tundish and discharge pipes should be fi tted in
accordance with the requirements and guidance
notes of Building Regulation G3. The G3 Requirements
and Guidance section 3.9 are reproduced in the
following sections of this manual. Information Sheet
No. 33 available from the British Board of Agrément
gives further advice on discharge pipe installation.
For discharge pipe arrangements not covered by
G3 Guidance or BBA Info Sheet No.33 advice
should be sought from your local Building Control
Offi cer. Any discharge pipe connected to the pres-
sure relief devices (Expansion Valve and Tempera-
ture/Pressure Relief Valve) must be installed in a
continuously downward direction and in a frost
free environment.
Water may drip from the discharge pipe of the
pressure relief device. 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.
G3 REQUIREMENT
"...there shall be precautions...to ensure that the hot
water discharged from safety devices is safely con-
veyed to where it is visible but will not cause danger
to persons in or about the building."
G3 GUIDANCE SECTION 3.9
The discharge pipe (D1)
book] 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 fi tted 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 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 fl ow resistance. Refer to Table 3,
6
[see fi g. 5 in this instruction
Table 1 and the worked example
5 in this instruction book].
An alternative approach for sizing discharge pipes
would be to follow BS 6700:1987 Specifi cation for design
installation, testing and maintenance of services sup-
plying water for domestic use within buildings and
their curtilages, Appendix E, section E2 and table 21.
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 and in a frost free
environment.
d. have discharges visible at both the tundish and the
fi nal point of discharge but where this is not possible or
is practically diffi cult there should be clear visibility at
one or other of these locations. Examples of acceptable
discharge arrangements are:
i. ideally below a fi xed 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, infi rm 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, roofi ng felt and non-metallic
rainwater goods may be damaged by such dis-
charges.
[see Table 3 and Fig.