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Figure 7-3: Sealed system components
7.5 SYSTEM MODELS
All System models have the following sealed system components
factory tted (refer to Figure 7-3):
• A diaphragm expansion vessel complying with BS 4814, pre-
charged at 1.0 bar. Refer to Section 2.2.
• System pressure gauge, with an operating range of 1 to 4 bar.
• Pressure relief safety valve complying with BS 6759 and set to
operate at 2.5 bar.
• Air vent, tted to the ow pipe of the boiler, ensures the boiler is
vented.
• Filling loop. This must be isolated and disconnected after lling
the system.
Refer to Section 2.2 for system volumes and BS 7074: for further
guidance and for further details of the expansion vessel.
For information on the circulating pump tted to sealed system
models, please refer to Appendix A1 or A2 as required at the back
of this installation and servicing manual.
The expansion vessel tted, is supplied with a charge pressure of
1.0 bar (equivalent to a maximum static head of 10.2 metres). The
charge pressure must not be less than the actual static head at
the point of connection.
! CAUTION !
Do not pressurise the vessel above 1.5 bar.
! NOTE !
The air pressure in the vessel must be checked annually.
The central heating system volume, using the expansion vessel
as supplied, must not exceed the recommended value. Refer to
Section 2.2. If the system volume is greater, an extra expansion
vessel (complying with BS 4841) must be tted as close as
possible to the central heating return connection on the boiler.
The charge pressure of the extra vessel must be the same as the
vessel tted in the boiler.
Refer to either BS 7074:1:1989 or The Domestic Heating
Design Guide for the required total expansion vessel volume
for the system concerned.
! NOTE !
The air charge pressure may be checked using a tyre
pressure gauge on the expansion vessel Schraeder valve.
The vessel may be re-pressurised using a suitable pump.
When checking the air pressure the water in the heating
system must be cold and the system pressure reduced to
zero.
Section 7: Sealed Systems
Pump isolating
valves
Pump
Heating flow
Heating return
Manual air
vents
Pressure
relief valve
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