EN • 4
662Y0600 • A
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The BG 2000-S burner is fitted with a gas valve – venturi assembly, an
electronic controller, a fan, a flame holder and lighting and ionisation
electrodes.
CONTROLLING THE AIR – GAS MIXTURE
As the fan sucks in air through the venturi, a drop in pressure (
P1
) is produced in
the neck of the venturi. The gas valve regulator then reacts to maintain a pressure
differential equal to the offset value between the pressure at the gas valve outlet
(
P2
) and atmospheric pressure (
P3
):
P2 – P3 = offset
If the air flow decreases,
P1
increases; the same occurs for
P2
;
P2
is then >
P3
;
the regulator
R
is moved higher to make
P2 – offset = P3
; pressure
P4
falls and
the valve
C
is turned down: the gas flow decreases.
By careful adjustment of the offset, an air – gas pressure ratio of 1 is obtained,
regardless of the fan speed.
The pressure differential between the venturi neck and the gas valve outlet then
causes gas to be sucked through the venturi.
The gas flow adjustment screw can be used to adjust the quantity of gas injected
for a given air flow, which will set the % CO
2
in the flue gas.
A given output can then be set simply by adjusting the speed of rotation of the fan
and the % CO
2
to preset values.
LIGHTING AND FLAME CONTROL
The burner control unit performs the tasks of lighting the burner by producing a
spark at the ignition electrode, and maintaining the flame when the gas valve is
opened by measuring the ionisation current.
The lighting sequence is shown in the diagram below: When the boiler thermostat
detects a demand for heat, the fan starts; after 10 seconds of preliminary flushing,
the gas valve is opened and simultaneously a spark is produced. If an ionisation
current is detected in the first 5 seconds, combustion occurs normally until the
end of the demand. If not, the gas valve is closed and the fan stopped, the burner
being in safety mode. It must then be reset manually before lighting is attempted
again.
Operating
Sequence of starting
Ionisation
Thermostat
Fan
Gas valve opens
Spark
0
5
10
15
20
Sec.
Pre-ignition
BG 2000-S 25 / 35 / 45 / 55 / 60 / 70
Ionisation
Thermostat
Fan
Gas valve opens
Spark
0
5
10
15
20
Sec.
Pre-ignition
BG 2000-S 100
Functional diagram
1. Air
2. Gas
3. Venturi
4. Fan
5. Offset adjustment screw
6. Gas flow a adjustement screw (CO
2
)
7. Air - gas mixture
1
7
2
5
R
3
4
6
P1
P2
P3
P4
C
