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20190798

Start-up, calibration and operation of the burner

5.6

Pressure switch adjustment

5.6.1

Air pressure switch

Adjust the air pressure switch (Fig. 32) after performing all other
burner adjustments with the air pressure switch set to the start of
the scale.
With the burner operating at MIN output, increase adjustment
pressure by slowly turning the relevant knob clockwise until the
burner locks out.
Then turn the knob anticlockwise by about 20% of the set point
and repeat burner start-up to ensure it is correct.
If the burner locks out again, turn the knob slightly anticlockwise.

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.

5.6.2

Maximum gas pressure switch

Adjust the maximum gas pressure switch (Fig. 33) 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.

5.6.3

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. 34) 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 stabilis-
er (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 al-
ways 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 com-
pletely the manual gas cock.

ATTENTION

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).
To check this, insert a combustion analyser into
the chimney, slowly close the fan suction inlet (for
example with cardboard) and check that the
burner locks out, before the CO in the fumes
exceeds 1%.

ATTENTION

1 kPa = 10 mbar

ATTENTION

Adjust the maximum gas pressure switch to
30 mbar

Fig. 32

D3854

PGM

Fig. 33

D3856

20181543

Fig. 34

D3855