baltur BT 75 DSNM-D, Instructions For Use Manual

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98323_201501
ENGLISH
ELECTRIC CONNECTIONS
The burner electrical connections have been kept to a minimum. We
recommend that all connections are made of flexible electric wire.
Electric lines must be installed at a suitable distance from hot parts.
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
sure that the main line, the relative fuse switch (fuses are essential)
and the limiting device, if any, are suitable for bearing the maximum
current absorbed by the burner.
DESCRIPTION OF OPERATION
During the fuel oil pre-heating stage, voltage passes through the pre-
heater regulation thermostat and reaches the coil of the resistances
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,
reaching 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 transformer 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
the nozzle. The moving back of the rods also closes the by-pass
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.