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Pressure stabilizes at around 27 bars because the pump pressure regulator is set at this value.
As soon as the atomized oil leaves the nozzle it is ignited by the spark from the electrodes. During
1st stage ignition the servomotor keeps the air fl ap in a set position according to the quantity of
fuel burnt. If a fl ame is ignited properly the shutdown position is passed, the ignition transformer is
switched off and the 2
Opening of the 2
2
stage nozzle (n° 4/1).
nd
The pressure of 25 bars (27 - 2 = 25) acts on the nozzle closure device of the 2
pressure of 16 bars, stops fuel fl owing to the second nozzle. This device is thus opened by the pressure
itself and the second nozzle starts working. A pressure of 25 bars now acts on the two nozzles. To read
off the effective pressure at the atomization unit and thus at the nozzles we recommend that you connect
the pressure gauge to the tank fi lter coupling (see drawing 0002932230).
NOTE: It is evident from the above that the choice of nozzles, as a function of total desired fl ow-rate (2 nozzles
working), must be made by taking into account the fl ow-rates corresponding to a working pressure of 25
bars. However, it is necessary to bear in mind that when the burner is working with the fi rst stage only the
fuel supply rate is that which corresponds to one nozzle only as a function of 25 bars pressure.
It is obviously possible to vary the "relationship" between the fi rst and the second stage extensively by
changing the nozzles. To ensure proper operation, always bear in mind that the fuel supply rate with the
fi rst stage must never be less than the model-specifi c minimum fl ow-rate (see identifi cation plate).
A lower fl ow-rate could make ignition diffi cult and combustion with the fi rst stage only may not be good.
NOTE: Some burner models have three nozzles (see drawing n° 0002900564). In this case there are two second
stage nozzles and both are subject to a pressure of 25 bars.
From the moment in which the fl ame appears in the combustion chamber the burner is controlled by the photo-
resistance and the thermostats. When the temperature or pressure reaches the levels set on the thermostat or
working pressure switch that device will shut down the burner. The unit resumes normal operation automatically
when the temperature/pressure falls by the necessary amount.
If, for any reason, the fl ame goes out while the unit is working a (second) photoresistance cuts power to the power
relay switch and opens it; this switches off the n° 7 preventilation solenoid valve which opens and rapidly vents
the existing pressure. The atomized oil spray is intercepted by automatic closure of the nozzle shutdown devices
on the atomizing unit as soon as pressure falls below their settings.
In this case (with OR 3/B control box) the ignition stage is automatically repeated and, if the fi rst stage is lit normally,
the burner starts working again normally too. If this is not the case (irregular or absent fl ame) the unit shuts down
automatically. With the LAL 1.25 control box an absent fl ame causes the burner to shut down without "attempting"
a second ignition. If the program is interrupted (power failure, manual work, tripped thermostat etc.) during the
preventilation stage the programmer goes to its home position and repeats the entire burner ignition sequence.
Burner
Control box and
Model
relative programmer
BT 40 DSN - 4T
BT 55 DSN - 4T
BT 75 DSN - 4T
BT 100 DSN - 4T
BT 120 DSN - 4T
BT 180 DSN - 4T
BT 250 DSN - 4T
BT 300 DSN - 4T
Cyclical relay
BT 350 DSN - 4T
TWO STAGE HEAVY OIL BURNER
stage n° 8 solenoid valve is switched on (closed in the home position).
nd
stage valve allows the fuel (at a pressure of 25 bars) to reach the closure device of the
nd
CONTROL BOX SPECIFICATIONS
Safety time
in seconds
OR 3/B
5
LOA 44
5
LAL 1.25
5
0006080415 ed2005/08
Preventilation time
in seconds
30
25
22,5
36 / 80
stage which, up to a
nd
Post-ignition
Time between 1st
in seconds
and 2nd stage
in seconds
5
5
5
5
15
7,5
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