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MODULATION OPERATION DESCRIPTION
The term modulation operation means that transition from the first
stage (minimum power) to the second stage (maximum power) and
vice versa, is progressive in terms of both amount of combustion air
let in and amount of output fuel, continuously adjusting to the specific
boiler requirements.
It is necessary to connect the modulation kit to be ordered as
accessory and the relevant temperature or steam pressure probe,
suitable for the specific type of boiler.
The burner control and command equipment is activated by means of
the switch on the panel (I).
The equipment carries out the ignition program by starting and
controlling the different burner components.
IMPORTANT
The air pressure switch must be adjusted upon ignition of
the burner according to the air pressure provided to the fan,
otherwise the equipment will shut down in "lock" condition.
From the pump, the fuel reaches the atomisation unit without flowing
out because both delivery and return are closed by pins located at
the rod ends.
The closing pins are pressed against the seats by robust springs
placed on the opposite ends of the rods.
Therefore, the fuel completes the pre-circulation phase passing
through the atomisation unit, the return pressure regulator, the pump
and from the latter it is discharged into the return system.
In the pre-circulation phase, the pressure value is some bar higher
than the minimum pressure to which the return pressure regulator is
calibrated (10 ÷ 12 bar).
The pre-ignition time is given by the total time of the operations below:
- fuel/air output servomotor opening stroke, 45 seconds;
- pre-ventilation time set in the equipment 22.5 seconds;
- closing stroke of fuel/air supply adjustment servomotor up to ignition
air position, approx. 40 seconds.
The total duration of the pre-ignition phase is about 107.5 seconds.
The equipment starts the ignition sequence by activating the relevant
transformer which, in turn, provides high voltage to the electrodes.
The electrodes cause the electric discharge for the ignition and after
2.5 seconds the equipment powers the magnet that draws back the
two fuel delivery and return rods of the atomisation unit.
The backward movement of the rods causes the passage (by-pass)
in the atomisation unit to close, and as a result, the pressure in the
pump reaches the fuel atomisation level of approx. 20 ÷ 22 bar.
The fuel passes through the nozzle at the suitable pressure to be
atomised.
The return pressure, which determines delivery to the furnace for the
ignition flow rate, is regulated by the return pressure regulator, about
10÷12 bar.
The presence of the flame is detected by the photoresistor.
After 5 seconds, the equipment moves past the lock-out position, cuts
power off the transformer and keeps the burner running at minimum
capacity.
If the temperature or pressure probe is set to a temperature or
pressure higher than that in the boiler, the adjustment servomotor is
enabled, gradually increasing the fuel and combustion air output up
to the maximum level the burner is set to.
The increase in the output of fuel is determined by the fuel / air
regulation control disk which, by rotating, causes greater compression
of the return pressure regulator spring and thus an increase in
pressure on the system return.
In order to obtain a proportional increase of fuel and air, it is necessary,
upon the first ignition, to work on the screws that change the profile of
the fuel /air regulation control disk.
The increase of fuel supply until maximum capacity is determined by
the return pressure regulator that reaches a maximum pressure of
18÷20 bar if the pump pressure is 20÷22 bar.
The burner remains in maximum supply position until the temperature
or pressure modulation probe reaches the value set for the boiler.
Now the modulation servomotor starts gradually reducing fuel and
combustion air supply until the minimum value.
If, even with minimum supply the temperature or pressure (in case
of steam boiler) of modulation probe intervention, the burner stops.
Summary of Contents for GI 350 DSPG
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