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Start-up, calibration and operation of the burner
6.6 Servomotor
The servomotor (Fig. 29) simultaneously regulates, through a
transmission system, air delivery and pressure and delivery of the
fuel in use.
It is fitted with adjustable cams which drive a similar number of
selector switches.
Cam 1: Sets the servomotor limit switch to max. posi-
tion (130° ca.).
(Oil operation).
Cam 2: Sets the servomotor limit switch to 0° position.
When the burner is off, the air damper is com-
pletely closed.
(Oil operation).
Cam 3: Regulates minimum modulation delivery.
It is factory calibrated in the 45°. (Oil operation
at minimum).
Cam 4: No utilized.
Cam 5: No utilized.
Rem. cam: No utilized.
Lever 7: Servomotor release.
6.7 Adjustment pressure switches
6.7.1 Air pressure switch - CO check
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. 30).
With the burner operating at minimum output, increase adjust-
ment 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.
The air pressure switch is fitted in an "absolute" mode, that is,
connected only to the pressure test point “+” 22) (Fig. 5).
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).
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%.
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