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DESCRIPTION OF OPERATION WITH LIQUID
FUEL
FURTHER INSTRUCTIONS TO START A MIXED BURNER
We recommend performing the first ignition with liquid fuel (fuel
change-over switch) because, in this case, the output is conditioned
by the nozzle that is used whereas the output of the natural gas can
be varied as required by adjusting the flow rate regulator.
It is not advisable to have too large a burner for the boiler for heating
and for hot water as the burner may work for long periods with a
single flame, making the boiler work at lower than required output; as
a result of this the combustion products (fumes) emerge at too low a
temperature (at about 180°C in the case of heavy oil and 130°C with
diesel fuel), causing soot to build up at the chimney outlet.
IMPORTANT
When the boiler is working at a lower output than that indicated
by the technicians, it is likely that acidic condensate and soot
will form in the boiler with the result that it will quickly corrode
and get clogged up.
When the two-flame burner is installed on a water boiler for heating
use, it must be connected so that it works normally with both flames,
completely stopping without passing to the first flame when the preset
temperature is reached.
To obtain this operating condition, do not install the second flame
thermostat and make a direct connection (bridge) between the
respective four pole plug terminals.
In this way only the burner’s capacity to switch on at low rate is used
for a gentle ignition, which is essential for boilers with a pressurised
combustion chamber and also very useful for normal boilers with
depression combustion chamber. The burner (start/stop) command is
subject to the usual operating or safety thermostats.
Closing the ON - OFF switch, if the thermostats are closed, the
voltage reaches the command and control equipment which starts
its operation cycle. This switches on the fan motor and the ignition
transformer.
The motor turns the fan that carries out an air wash of the combustion
chamber and, at the same time, the fuel pump that causes circulation
in the ducts, expelling any gas bubbles through the return valve. This
pre-wash stage ends with the opening of the safety and first stage
solenoid valves, which allows the fuel at a pressure of 12 bar to get to
the first stage nozzle and from this to enter the combustion chamber
finely atomised.
As soon as the atomized fuel exits the nozzle, it is set on fire by the
spark present between the electrodes since the start of the motor.
During first stage ignition, the air gate is held in the adjusted position
on the special air/gas adjustment servomotor cam.
If the flame appears regularly, after the safety time foreseen by the
device, it starts the air/gas regulation servomotor that moves to the
second stage position. During the transition from the first to the
second stage, the servo motor operates the solenoid valve (normally
closed) of the second stage.
The opening of the second stage valve allows the diesel to reach the
second nozzle and the burner to operate at full capacity.
Once the flame appears in the combustion chamber, the burner is
controlled and commanded by the flame control equipment and by
the thermostats.
The control equipment follows the program and switches the ignition
transformer off. When the temperature or the pressure in the boiler
reaches that set by the thermostat or pressure switch, the latter stops
the burner.
Subsequently, if the temperature of pressure decreases below the
lower thermostat or pressure switch threshold value, the burner will
switch on again.
If, for any reason, the flame is lost during burner operation, the flame
control device immediately cuts off the power and automatically
switches off the solenoid valves which intercept the nozzle flow.
The ignition phase is repeated in this manner and, if the flame
reignites normally, the burner will return to normal operation.
Otherwise (irregular flame or no flame), the equipment will shut-down
automatically.
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