20098208
22
GB
Start-up, calibration and operation of the burner
6.5
Servomotor adjustment
The servomotor (Fig. 26) adjusts simultaneously, by cross-refer-
encing, the flow rate and pressure of the air and flow rate of the
fuel in use.
It is equipped with adjustable cams which operate the same num-
ber of switches.
Cam I:
limits the limit switch of the servomotor on po-
sition max (approx. 130°).
Cam II:
limits the limit switch of the servomotor on po-
sition 0. With the burner off, the air damper is
completely closed.
Cam III:
regulates the minimum modulation output; fac-
tory set at 45°.
Remaining cam: not used
Lever 7:
servomotor reset
6.6
Air / fuel adjustment
Fuel/combustion air is synchronized by means of a servomotor
(Fig. 27) that, connected to a variable-profile cam, operates the
outlet air dampers and, by means of suitable linkage, the com-
bustion head and gas butterfly valve.
To reduce pressure loss and to have a wider adjustment range,
it is best to set the servomotor to the maximum output used, as
near to maximum opening (130°) as possible.
On the gas butterfly valve, the fuel’s partial setting adjustment
based on required output, with the servomotor fully open, is made
by using the pressure stabilizer on the train.
6.6.1
Max output
Adjustment of air delivery
Set the servomotor to maximum opening so that the air dampers
are fully open.
To reduce output, loosen screw 2)(Fig. 28) under the burner’s in-
take and close grille 1) progressively until you achieve the re-
quired output.
The only time reducing intake to a partial setting is not necessary
is when the burner is working at the top of the operating range
given on page 8.
Fig. 26
S8446
7
WARNING
We recommend you achieve the maximum output
required manually, and adjust intake to the partial
setting, define gas pressure and adjust the com-
bustion head before completing the setting.
Fig. 27
D7966
Fig. 28
D3094
