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5.12 Sealed water Systems
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.
5.13 Safety Valve
A safety valve must be fitted 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
fittings and positioned so that any discharge can be seen.
5.14 Expansion Vessel
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.
NOTE: 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.
5.15 Pressure Gauge
A pressure gauge with a set pointer and covering at least 0 to
4 bar (0 to 60 lb/in2) shall be fitted permanently to the system
in a position where it can be seen when filling the system.
5.16 Domestic Hot Water Cylinder
SINGLE FEED INDIRECT CYLINDERS ARE NOT SUITABLE
The domestic hot water cylinder must be of the double feed
fully indirect coil type. It must be suitable for working at a
gauge pressure of 0.35 bar above the safety valve setting.
5.17 Water Makeup
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 filling loop.
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