Electric Connections - baltur BT 75 DSNM/D Manual De Instrucciones

ELECTRIC CONNECTIONS

E
The burner electrical connections have been kept to a minimum. We
N
recommend that all connections are made of flexible electric wire.
Electric lines must be installed at a suitable distance from hot parts.
G
Make sure that the electric line you wish to connect to the apparatus
is fed with voltage and frequency values suitable for the burner. Make
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sure that the main line, the relative fuse switch (fuses are essential)
I and the limiting device, if any, are suitable for bearing the maximum
current absorbed by the burner.
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DESCRIPTION OF OPERATION (
H
During the fuel oil pre-heating stage, voltage passes through the
pre-heater regulation thermostat and reaches the coil of the resi-
stances remote switch. This remote switch shuts and takes current
to the pre-heater resistances, which heat the fuel contained in the
pre-heater. The resistances heating the pump, the unit for atomizing
fuel and regulating first-flame return pressure are also cut-in, through
the panel ( I ) switch.
The pre-heater minimum level thermostat shuts off when the
temperature reaches the value at which the pre-heater is set. The
equipment is only cut-in when the temperature at which resistances
are cut-out (opening of the regulation thermostat contact) is reached
in the pre-heater. This is therefore achieved when fuel oil in the
pre-heater is at maximum temperature. The burner control box (a
cyclic relay) is then cut-in by the heating tank regulation thermostat
when the latter cuts-out the resistances by switching off the relative
remote switch.
The control box cyclic relay carries out the ignition programme, by
putting into operation the fan motor for executing the preventilation
stage. If the pressure of the air supplied by the fan is sufficient to
put the relative pressure switch into action, cutting in also occurs
of the motor of the pump that carries out hot oil pre-circulation in
the burner pipes.
Oil from the pump reaches the pre-heater, passes through it, re-
aching the temperature envisaged, exits through a filter and then
reaches the atomizing unit. The oil circulates in the atomizing unit
without flowing out of the nozzle because the channels leading
towards the nozzle (outward flow) and from the nozzle (return flow)
are closed. Closure is carried out by "closing cones" fixed to the
rod ends. These "cones" are pressed against their seats by strong
springs located at the opposite end of the rods. Oil circulates and
flows out of the return end of the atomizing unit, passes through
the trap where the TRU thermostat is and reaches the 1st flame
return pressure regulator, passes through it, goes through the 2nd
flame solenoid valve (usually open), reaches the pump return pipe
and from this it discharges into the feed system return pipe. Hot
oil circulation as described above is carried out at slightly higher
pressure (a few bar) compered to the minimum pressure at which
the 1st flame return pressure regulator is set (10 ÷ 12 bar). This oil
precirculation and preventilation phase lasts 22,5 seconds. This
time can be prolonged (infinitely, in theory) because the electric
circuit is built in such a way that it does not enable the control
box to continue carrying out the ignition programme, until the fuel
temperature, in the nozzle return piping, has reached the level at
which the TRU thermostat is set. This particular design does not
allow fuel to pass through the nozzle until the fuel itself reaches at
least the temperature at which the TRU thermostat is set. Usually,
the TRU thermostat operates within normal preventilation time (22,5
seconds), otherwise the fuel oil preventilation and pre-circulation
stages are prolonged until the TRU goes into action. TRU operation
(oil circulating is sufficiently hot) enables the control box to continue
executing the ignition programme, by cutting-in the ignition transfor-
mer which feeds high voltage to the electrodes.
High tension between the electrodes triggers the electric charge
(spark) to ignite the air-fuel mixture.
2,5 seconds after the ignition spark begins, the control box takes
voltage to the magnet which, through suitable levers, moves back
the two rods that intercept the flow of fuel (outgoing and return) to
BT 8713/1) the nozzle. The moving back of the rods also closes the by-pass
SEE
inside the atomizing unit, and consequently pump pressure reaches
the normal level of about 20 ÷ 22 bar. Withdrawal of the two rods
from the closure seats now enables fuel to enter the nozzle at a
pressure of 20 ÷ 22 bar set at the pump and to exit the nozzle,
sufficiently atomized.
Return pressure, which determines oil flow to the combustion
chamber, is now regulated by the 1st flame return pressure regulator.
This value is about 10 ÷ 12 bar for the 1st flame (minimum output).
Atomized fuel exiting from the nozzle, mixes with the air supplied
by the fan and is ignited by the spark at the electrodes.
Flame presence is detected by the photoresistance.
The programmer continues and after 5 seconds, overcomes the
locking position, turns off ignition and then, commands 2nd flame
cut-in.
This operation takes place by feeding current, through the relative
thermostat or pressure switch, to the motor that controls the air inlet
in the position corresponding to the 2nd flame.
Rotation of the air motor shaft allied to a suitable cam closes a
contact which feeds voltage to the coil of the 2nd flame solenoid
valve. This valve closes and thus intercepts fuel flow through the
1st flame return pressure regulator.
Return fuel is now compelled to flow through the 2nd flame pressure
regulator and return pressure rises up to the set level of the regulator.
As a result, nozzle output increases and the burner now operates
at maximum capacity.
Nozzle return pressure is about 18 ÷ 20 bar if pump pressure is
20 ÷ 22 bar.
Fuel and comburent air output stay at maximum level until the boiler
temperature (pressure if it is a steam boiler) reaches the level set at
the 2nd flame thermostat (pressure switch in case of steam boilers)
and operates the thermostat by bringing the 1st flame back into
operation. The return movement to the 1st flame position causes a
reduction of fuel output and relative combustion air.
The 1st flame on its own is not usually enough to keep pressure or
temperature at the desired value and therefore, pressure diminishes
until it reaches the level at which the 2nd flame control device
(pressure switch or thermostat), again cuts in air and fuel flow totally.
The burner stops operating completely when, even with just the 1st
flame cut-in, pressure or temperature reaches the intervention level
of the relevant control device (pressure switch or thermostat). The
apparatus re-ignites automatically when pressure or temperature
drops below the level at which the pressure switch or thermostat
has been set.
Please note that the output variation range with good combustion is
roughly from 1 to 1/3 compared to the maximum specified output.
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