Glow-worm Flexicom hx - Manual (Page 17)

0020107230_04 - 12/14 - Glow-worm
INSTALLATION
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Water System - Sealed Central Heating
System
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 5.4 for a suggested layout.
5.13 Safety Valve
A safety valve must be fi 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 fi ttings
and positioned so that any discharge can be seen.
Diagram 5.4
14017
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 con-
nected at a point close to the inlet side of the circulating pump,
see the diagrammatic layout, diagram 5.4.
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 cur-
rent 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.
Guidance on vessel sizing is also given in the current issue of
BS5449 and BS7074 Part 1, for 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.