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5.6
Pressure switch adjustment
5.6.1
Air pressure switch
Adjust the air pressure switch after performing all other burner
adjustments with the air pressure switch set to the start of the
scale (Fig. 30).
With the burner operating in 1st stage, increase adjustment
pressure by slowly turning the relevant knob clockwise until the
burner locks out.
Then turn the knob anti-clockwise by about 20% of the set point
and repeat burner starting to ensure it is correct.
If the burner locks out again, turn the knob slightly anticlockwise.
As a rule, the air pressure switch must limit the CO
in the fumes to less than 1% (10,000 ppm).
To check this, insert a combustion analyser into
the chimney, slowly close the fan suction inlet (for
ATTENTION
example with cardboard) and check that the
burner locks out, before the CO in the fumes
exceeds 1%.
The incorporated air pressure switch can work in a 'differential'
mode if connected with two pipes.
If a strong depression in the combustion chamber during the pre-
purging phase does not allow the air pressure switch to switch,
this can be obtained by applying a second tube between the air
pressure switch and the suction inlet of the fan.
In this way, the pressure switch will work in differential mode.
The use of the air pressure switch with differential
operation is allowed only in industrial applications
and where rules enable the air pressure switch to
control only fan operation without any reference to
ATTENTION
CO limit.
D3951
Start-up, calibration and operation of the burner
D794
Fig. 30
5.6.2
Minimum gas pressure switch
The purpose of the minimum gas pressure switch is to prevent
the burner from operating in an unsuitable way due to too low gas
pressure.
Adjust the minimum gas pressure switch (Fig. 31) after having
adjusted the burner, the gas valves and the gas train stabiliser.
With the burner operating at maximum output:
install a pressure gauge downstream of the gas train stabiliser
(for example at the gas pressure test point on the burner
combustion head);
choke slowly the manual gas cock until the pressure gauge
detects a decrease in the pressure read of about 0.1 kPa
(1 mbar). In this phase, verify the CO value which must always be
less than 100 mg/kWh (93 ppm).
Increase the adjustment of the gas pressure switch until it
intervenes, causing the burner shutdown;
remove the pressure gauge and close the cock of the gas
pressure test point used for the measurement;
open completely the manual gas cock.
1 kPa = 10 mbar
ATTENTION
5.6.3
Flame presence check
The burner is fitted with an ionisation system to check that a
flame is present. The minimum current required for the control
box operation is 6 A.
The burner supplies a significantly higher current value, so that
no check is usually needed.
However, if it is necessary to measure the ionisation current,
disconnect the plug-socket on the ionisation probe cable and
insert a direct current microammeter with a base scale of 100 A.
Carefully check polarities.
D3843
27
GB
D3855
Fig. 31
µA
10
RMG
Fig. 32
20191684
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