0020107233_00 - 06/11 - Glow-worm
INSTALLATION
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The boiler must be supplied from an unrestricted water
supply taken from a feed and expansion cistern situated at a
maximum height of 27 metres (90ft) above the boiler.
The cold feed must be 15mm minimum size.
The vent must rise continuously and be unrestricted.
It is important that the relative positions of the pump, cold feed
and open vent are as shown in diagram 5.2.
For combined feed and vent, a 22mm pipe must be tted in
accordance with BS 5449.
The installation must comply with the appropriate
requirements of the current issue of BS4814, BS5449,
BS6759, BS6798 and BS7074 Part 1 and 2.
See diagram 5.3 for a suggested layout.
A safety valve must be tted to a sealed system. It shall
be preset, non-adjustable with a lift pressure of 3 bar,
incorporating seating of a resilient material, a test device and
a connection for drain.
The drain from the safety valve must be routed outside the
building, must not discharge above an entrance or window
or any type of public access area, be clear of any electrical
ttings and positioned so that any discharge can be seen.
A diaphragm type expansion vessel, conforming to the current
issue of BS4814 (see also BS7074 Part 1 and 2) must be
connected at a point close to the inlet side of the circulating
pump, see the diagrammatic layout, diagram 5.3 unless laid
down differently by the manufacturer.
The expansion vessel volume depends on the total water
system volume and the initial system design pressure. For
any system an accurate calculation of vessel size is given in
the current issue of BS5449 and BS7074 Part 1.
Example: For an initial design pressure of 0.7 bar, the
minimum total vessel volume required is 0.063 x Total System
Volume.
A higher initial design pressure requires a larger
volume expansion vessel.
In GB, guidance on vessel sizing is also given in the current
issue of BS5449 and BS7074 Part 1.
In IE refer to the current edition of I.S.813 “Domestic Gas
Installations”.
The charge pressure must not be less than the static head
of the system, that is, the height of the highest point of the
system above the expansion vessel.
A pressure gauge with a set pointer and covering at least 0 to
4 bar (0 to 60 lb/in2) shall be tted permanently to the system
in a position where it can be seen when lling the system.
Diagram 5.2
13147
Provision should be made for replacing water loss from the
system using a make up bottle mounted in a position higher
than the top point of the system, connected through a non-
return valve to the return side of either the heating circuit or
the hot water cylinder. Alternatively, provision for make up can
be made using a lling loop.
Provision for lling the system at low level must be made, see
diagram 5.4. There must be no permanent connection to the
mains water supply, even through a non-return valve.
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