baltur BT 250 DSG Mode D'emploi page 28

DESCRIPTION OF OPERATION (See 0002900600)
By closing the switch on the burner, and if the thermostats (control and safety) allow it, current flow to the control
box and activate the motor and the ignition transformer.
The motor will start up the fan which will carry out a pre-ventilation with air from the combustion chamber and
simultaneously the pump which will drive oil through the pipes and expel any gas bubbles through the return pipe.
During the pre-ventilation phase the combustion air shutter is activated by its motor and opens in the 2nd flame
position (pre-ventilation with air open).
Subsequently, the air shutter returns to the 1st flame position for ignition.
This "pre-washing" cases when electrovalve no. 1 closes (open in the rest position) and this interrupts the free
discharge of oil towards the cistern.
When electrovalve no. 1 closes, an increase in pressure in the delivery pipes follows.
When the light oil pressure reaches 7 bar, the mechanical valve which can be found in the atomizer unit opens
allowing oil to reach the 1st flame nozzle and come out of it into the combustion chamber finely atomized. The
pressure stabilises at about 10 bar because the 1st flame pressure regulator has been set at this value. As soon
as atomized oil comes out of the nozzle, it is ignited by the spark between electrodes which has been present
since the motor started up.
If the flame appears regularly, the programmer passes over the "shut down" position and inserts the motor which
activates the combustion air shutter and puts it in the 2nd flame position.
While this is happening, an adjustable cam activated by the same motor, closes the electrical contact which takes
voltage to electrovalve no. 2 which intercepts the flow of oil through the 1st flame pressure regulator. The 1st
flame pressure regulator is excluded in this way and the pressure increase until it reaches the value at which the
pressure regulator incorporated in the pump has been set (16 bar).
The 16 bar pressure also acts on the mechanical valve which, up to a pressure value of 13 bar, prevents the fuel
from flowing to the second nozzle.
This valve is opened in this way by the pressure, and the second nozzle also starts operating.
The 16 bar, pressure now acts on the two nozzles.
When the unit is working at a pressure of 16 bar, it is operating at maximum capacity.
Note: From the above outline it is evident that the choice of nozzles with respect to the desired total burner output
(2 nozzles in operation) should be made taking into account the delivery rates corresponding to the light oil
16 bar, operating pressure.
It should be noted, however, that when the burner operates only with the 1st flame, the delivery rate of the
first nozzle corresponds to the values given in the 10 bar, pressure table because the pressure regulator for
the 1st flame is set at this value.
Obviously, it is possible to change the ratio between the 1st and 2nd flame within a wide range by replacing
the nozzles. However, it should be remembered that for efficient operations the fuel supply for the 1st
flame should not be less than the minimum burner output (shown on the name-plate) for each specific
model. A smaller output could make ignition difficult, and combustion with the 1st flame only might not be
satisfactory.
From the moment the flame appears in the combustion chamber, the burner is controlled and monitored by
the photoresistant cell and thermostats, the programmer continues its cycle and disconnects the ignition
transformer; consequently the burner is "on" and operating at full rating. If the programme is interrupted
(voltage failure, manual operation, thermostat tripping, etc.) during the pre-washing phase, the programmer
will return to its original position and automatically repeat the whole burner start-up cycle. When the tem-
perature or pressure reaches the value preset on the thermostat or operating pressure switch, its tripping
will cause the burner to stop. The burner will resume its operation automatically when the temperature or
pressure value falls by the required amount.
In case of flame failure during operations, the photoresistant cell will trip immediately (1 second) and stop
current to the relay which then opens and consequently disconnects the washing electrovalve. This in turn
rapidly discharges the existing pressure and the jet of atomized oil is cut off by the automatic closure of the
atomizing unit valve as soon as the pressure drops below 7 bar. In this case, the start-up cycle is repeated
automatically and if the flame ignites normally again, the burner will also resume its normal operations.
If there is a poor flame or no flame at all, the unit goes automatically to "shut down".
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