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7.7.5
Air pressure switch
Adjust the air pressure switch after having performed all other
burner adjustments with the air pressure switch set to the start of
the scale (Fig. 42).
With the burner operating at min. output, increase adjustment
pressure by slowly turning the relative 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 anti-clockwise a little
bit more.
As a rule, the air pressure switch must prevent the
air pressure from lowering below 80% of the ad-
justment value as well as preventing the CO in the
fumes from exceeding 1% (10,000 ppm).
WARNING
To check this, insert a combustion analyser into
the chimney, slowly close the fan suction inlet (for
example with cardboard) and check that the burn-
er locks out, before the CO in the fumes exceeds
1%.
The air pressure switch is of the differential type. If a negative
pressure in the combustion chamber during pre-purging prevents
the air pressure switch from closing, fit a tube between the air
pressure switch and the suction inlet of the fan.
The use of the air pressure switch with differential
operation is allowed only in industrial applications
and in places where national rules enable the air
pressure switch to control only fan operation.
WARNING
D521
1 kPa = 10 mbar
WARNING
7.8
Gas combustion checks
CO
2
It is better to set the burner with CO
3
Pci 8600 kcal/m
).
This way avoiding a loss of calibration setting (for example draft
variation) that could cause combustion with little air and the pro-
duction of CO.
CO
It must be not higher than 100 mg/kWh.
Start-up, calibration and operation of the burner
Fig. 42
not higer than 10% (gas with
2
7.7.6
Maximum gas pressure switch
Adjust the maximum gas pressure switch after having performed
all the other burner adjustments with the maximum gas pressure
switch set at the end of the scale (Fig. 43).
With the burner operating at MAX output, reduce the adjustment
pressure by slowly turning the relative knob anticlockwise until
the burner locks out.
Then turn the knob clockwise by 0.2 kPa (2 mbar). and repeat
burner firing.
If the burner locks out again, turn the knob again clockwise by 0.1
kPa (1 mbar).
7.7.7
Minimum gas pressure switch
Adjust the minimum gas pressure switch after having performed
all the other burner adjustments with the pressure switch set at
the start of the scale (Fig. 44).
With the burner operating at MAX output, increase adjustment
pressure by slowly turning the relative knob clockwise until the
burner locks out.
Then turn the knob anti-clockwise by 0.2 kPa (2 mbar) and repeat
burner starting to ensure it is uniform.
If the burner locks out again, turn the knob anti-clockwise again
by 0.1 kPa (1 mbar).
31
GB
D66
D896
Fig. 43
Fig. 44
20034985
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