FireBird HEAT PAC 120/150, Installation Servicing & Operating Instructions, Page: 35 / 56

A manually adjustable red pointer is also fitted on the protective
glass of pressure gauge. This has a screwdriver slot. When
system is cold and filled to Initial Fill Pressure Pi this pointer
should be rotated to read exactly as black pointer on dial.
This should not be subsequently altered. If system pressure,
as indicated on black pointer on dial, falls
below that indi-
cated by red pointer when system and boiler are cold this
means that Initial System Fill Pressure has dropped. Refill
system until indicated pressure rises to the same as red
pointer indicates - in this case 0.7 bar, as shown on
accompanying pressure gauge sketch. Sketch also shows
black pointer indicating maximum final system design
pressure (Pf).
N.B. Initial System Design Pressure (measured in
bar) equals static head of system (measured in bar) plus 0.3.
* A 12 or 14 litre expansion vessel is fitted to boiler, precharged with air or nitrogen to 1 bar which
allows a system static head of 5 metres. If the static head is greater than this then the air charge
in the vessel must be increased to balance the higher static head.
The air charge should not
exceed a pressure of 1.5 bar.
The Firebird Boiler with a built in Expansion Vessel’s having an initial air charge pressure of 1 bar.
If total water content of system is greater than the capibilities of the vessel supplied then an
additional vessel will be required to be fitted to the return pipe as close as is practicable to the
boiler. There should be no valves or restrictions between vessel and boiler.
See page 34 for vessel sizes.
If static head is altered then it is also necessary to alter air charge pressure to equal static head
(+ 0.3 Bar). This is necessary in order to keep system water from entering expansion vessel until
system is being heated and thus allow its maximum acceptance volume (V) to be used
only to
accommodate the expansion of system water during boiler operation.
Remember that air charge pressure must be equal in both vessels (attached to the same
system). In the above example this is 1 bar. Air charge pressure is the air pressure in expansion
vessel before system is filled. It is measured with a tyre gauge attached to Schrader valve on the
vessel.
N.B. N.B. With heating system up to full working temperature, if the final system
design pressure (Pf) reads more than 2.6 bar, as indicated on control
panel pressure gauge, then it is likely that:
(a) Total system water content is greater than that calculated and if
additional expansion vessel has been fitted it should be replaced
with a larger unit
OR if integral boiler expansion vessel only is used then an
additional expansion vessel is required.
(b) Static head may be higher than calculated. In this case it is
necessary to re-measure static head and revise expansion vessel
air charge pressure.
(C) Expansion vessel incorrect size or air charge pressure incorrect.
Refer to BS 7074 Part 1 and BS 5449 for further information.
33
B
A