26
CONTROL BOX SPECIFICATIONS
DESCRIPTION OF OPERATION
By closing the switch on the burner, and if the relative thermostat will allow it, the resistances relay will be connected.
Voltage will reach the thermostat that commends the resistances by passing through the boiler thermostat(s); therefore
these thermostats must be closed.
Control of the resistances through the boiler thermostat is to avoid the fuel oil boiling during the control box's pauses in
operations, and to avoid an unnecessary waste of electricity.
When the resistances have been connected in this way, they will heat the fuel oil in the pre-heater tank.
When the oil has been heated sufficiently, the minimum thermostat closes.
When the minimum thermostat has been closed, if the other (regulation and safety) thermostats allow it, voltage will
reach the control box which will start functioning and connect the burner component devices according to its programme.
The burner's motor will be turned on at the same time as the ignition transformer.
The motor starts up the fan, which will carry out a pre-ventilation with air from the combustion chamber; simultaneously;
the pump which circulates hot oil in the pipe system, expels cold oil and any gas bubbles through the return pipe.
This pre-ventilation and pre-washing phase lasts for 30 seconds and cases when the electrovalve closes (open in the
rest position) and this interrupts the free discharge of oil towards the cistern.
When the electrovalve closes, an increase in pressure in the delivery pipes follows.
Ehen the pressure reaches 12,5 bar, the mechanical valve which can be found in the atomizer unit opens, oil reaches
the nozzle and comes out of it into the combustion chamber finely atomized.
The pressure remains at about 22 bar because the pump's pressure regulator has been set at this value.
Note: The nozzle must be chosen considering the capacity valves corresponding to an operation pressure equal to 20
bar because there is a pressure drop (
,
p = 2 bar) caused by the antigas valve installed on the pre-heater filter.
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, the "shut down" position is passed over and the ignition transformer
is then disconnected. From the moment that the flame appears in the combustion chamber, the burner is commanded
and controlled by the photoresistant cell and the thermostats.
When the boiler temperature or pressure reaches the limit set on the thermostat or pressure switch, the burner will
stop. Subsequently, when the temperature or pressure drops below the re-closing limit set on the thermostat or
pressure switch, the burner starts up again.
To have increased safety, it is possible to install two control thermostats or pressure switches (a reserve one) regulated
at different values so that if the one regulated at a lower level does not work properly, the reserve one will intervene and
bring the burner to a standstill.
Even if the safety devices have come into action, the unit starts functioning again automatically when the temperature
or pressure drops low enough. If for any reason during operations there should be flame failure, the photoresistant cell
will intervene immediately (in one second) and interrupt the supply of the washing electrovalve which will open and
rapidly discharge the pressure existing in the tank; the atomized oil spray will be intercepted by the atomizer unit valve
closing automatically, as soon as the pressure has dropped below 12,5 bar..
The start-up cycle is repeated with pre-ventilation and pre-washing and, if the flame ignites again normally, the burner
will resume its normal operations. If it does not, (irregular flame or missing flame) the unit goes, automatically to shut
down. If the programme is interrupted (voltage failure, manuel or thermostat intervention) during the start-up cycle and
subsequently re-connected (return of voltage, manual or thermostat intervention etc.) the control box will automatically
repeat from the beginning the burner's start-up cycle.
While the burner is operating, the resistances are connected and disconnected according to the requirements by the
relative thermostat, and this is indicated by a yellow light fitted on the burner.
Burner
model
BT 15 N
BT 22 N
BT 35 N
BT 60 N
Control Box
OR 3/B
LOA 44
LAL 1.25
on demand
Safety time
in seconds
5
5
5
Pre-ventilation and
Pre-washing time
in seconds
30
25
22,5
Post-ignition
in seconds
5
2 ÷ 5
15
Содержание BT 15 N
Страница 23: ...23 Viscosity Temperature Diagram...
Страница 54: ......
