35
ENGLISH
DESCRIPTION OF HOW THE TWO FLAME BURNERS OPERATE
(see diagram)
The two stage burner always ignites with a limited amount of air and fuel (1st flame) and, subsequently, after a few seconds, it will
switch to full air and fuel operation (2nd flame). The ignition of the 2nd flame is subject to the consent of the control box and control
device (pressure switch or thermostat). When the burner works at full rating it will remain in this position until it reaches the pressure
or temperature limit pre-set on the control device (pressure switch or thermostat). The control device trips, disconnecting the 2nd
flame (fuel and air), when the limit to which it has been pre-set is reached. Then the burner works only with the 1st flame. Normally
the 1st flame alone is not sufficient to keep the temperature or the pressure at the desired limit, and so it will decrease until it reaches
the limit to which the control device of the 2nd flame (pressure switch or thermostat) reactivates the total fuel and air delivery rate. If
the burner operates only with the 1st flame will stop completely when the pressure or the temperature reaches the tripping point set
on the control device (pressure switch or thermostat). The burner starts up automatically again when the pressure or temperature
falls below the limit to which the pressure switch or thermostat has been pre-set.
Remarks: When a two stage burner is installed on a boiler for heating purposes, it should be connected so that it will normally
operate with both flames and stop completely, without switching to the 1st flame, when the pre-set temperature is reached. If
the burner operates (sometimes for long periods of time) with one flame only and the boiler is insufficiently loaded, consequently
combustion products come out at a very low temperature (less than 180 °C) and foul up the chimney outlet with soot. When
the boiler is insufficiently loaded, acid condense and soot are likely to build up in the boiler resulting in fast clog-up and
corrosion of the same. For this specific operation, do not fit the thermostat for the 2nd flame and make a direct connection
(bridge) between the respective terminals on the electric equipment. This uses only the burner capacity to ignite at a reduced
output which ensures a smooth lighting up, an essential condition for boilers having an over pressure combustion chamber,
yet very useful also in normal boilers (vacuum combustion chamber). The burner control is subject to the usual operating and
safety thermostats.
Unless prevented by the thermostats (regulation and safety), tripping the switch on the burner will power the control box causing the
motor and ignition transformer to cut in. The motor sets in motion the following parts: the fan washing out the combustion chamber
with air, the fuel pump which circulates fuel through the ducts, venting any gas through the return. This initial pre-washing phase is
terminated when the solenoid valve (safety and first flame) opens, sending the fuel at 12 bar to the nozzle (1st flame nozzle). The
latter, then, sends the finely pulverized fuel into the combustion chamber. As soon as this pulverized fuel is released from the nozzle
it is ignited by the spark which has been arcing between the electrodes since the motor was turned on. When the first flame is being
ignited, the air gate is kept in the position regulate by the special screw. This screw is accessed by removing the plug located on the
upper part of the hydraulic control piston (see BT 8614, or if a hydraulic air regulation servomotor is used, BT 8711/1 or BT 8653/1).
If the flame is ignited properly, after the safety period set by the control box, the solenoid valve for the second flame cuts in (it is closed
when not in use) (if a the air supply is servomotorized see BT 8711/1 or BT 8653/1).
Opening the valve to the 2nd flame allows the diesel fuel, at a pressure of 12 bar, to reach the 2nd nozzle. At the same time the
combustion air regulation piston moves downward, further opening the regulator. The piston stroke can be adjusted using the special
screw equipped with locknut. At this point the burner is in full operation. Once a flame appears in the combustion chamber, the burner
is controlled by the photoelectric resistance and by the thermostats. The control box runs the program and turns off the ignition
transformer. When the temperature or pressure in the boiler reaches the set points, the thermostat or pressure switch will cut in to
shut down the burner. Subsequently, when the temperature or pressure drops below a set value, the thermostat or pressure switch
will cause the burner to cut in once more. If, during operation, the flame goes out for any reason, the photoelectric resistance will
immediately cut out ( 1 second ) turning off the power supply to the relay. This automatically trips the solenoid valve thus cutting off
flow to the nozzles. At this point the ignition phase is repeated and, if the flame lights without difficulty, normal burner function is
restored. If it this is not the case ( if the flame is irregular or does not ignite at all ), the apparatus is automatically locked out.
If the program is interrupted (by a clack-out, manual intervention, thermostat trip, etc.) during the pre-wash phase, the programmer
returns to its initial position and the entire burner ignition phase is automatically repeated.
Note: It is clear from the above that, depending on the total capacity desired (with 2 nozzles operating), the choice of nozzle must
be made considering a fuel working pressure of 12 bar. Obviously, it is possible to change the relationship between the first
and second flame over a broad range by replacing the nozzle. One must always recall that for the unit to operate well, with a
single flame the fuel flow must never drop below the minimum capacity for the specific model (which can be read on the label).
A lower flow would make it difficult to ignite the flame, moreover, in this case, single flame combustion might not be good.
Control box specifications
Control box and
Safety time
Preventilation and
Post-starting
`time between
relativ programmer
in seconds
washing time
in seconds
1st e 2nd flame
OR 3/B
5
30
5
5
LOA 21-24
10
13
15
15
LOA 44
5
25
5
5 ÷ 8
LAL 1.25
5
22,5
5
7,5
GF 2 N
5
25 ÷ 30
10
10 ÷ 15
