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6.8
Pressure switch adjustment
6.8.1
Air pressure switch
The air pressure switch is set after all other adjustments have
been made. Begin with the switch at the start of the scale. With
the burner operating, increase adjustment pressure by slowly
turning the relevant knob clockwise until the burner stops. Then
turn the knob anticlockwise by 0.1 kPa (1 mbar) and repeat
burner start-up to ensure it is operating regularly.
If the burner locks out again, turn the knob again anti-clockwise
by 0.5 mbar.
In conformity with the standard, the air pressure
switch must prevent the air pressure falling below
80% of the adjusted value and the CO in the flue
gases exceeding 1% (10,000 ppm).
ATTENTION
To check this, insert a combustion analyser in the
flue, slowly reduce the burner air setting (for
example with a piece of cardboard) and verify that
the burner locks out before the CO value in the
flue gases exceeds 1%.
6.8.2
Maximum gas pressure switch
Adjust the maximum gas pressure switch (Fig. 32) after making
all other burner adjustments with the maximum gas pressure
switch set to the end of the scale.
To calibrate the maximum gas pressure switch, open the tap and
then connect a pressure gauge to its pressure test point.
The maximum gas pressure switch must be regulated to a value
no higher than 30% of the measurement read on the gauge when
the burner is working at maximum output.
After making the adjustment, remove the pressure gauge and
close the tap.
6.8.3
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. 33) 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 stabili-
ser (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 in-
tervenes, 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
20176605
Start-up, calibration and operation of the burner
D3854
D3856
D3855
32
GB
Fig. 31
PA
20181543
PGM
Fig. 32
Fig. 33
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