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DESCRIPTION OF TWO STAGE PROGRESSIVE
OPERATIONS WITH FUEL OIL (See 0002901490)
We refer a two-stage progressive operation because the passage
from the 1st flame to 2nd flame (from the minimum rate to the
maximum pre-established rate) takes place gradually and therefore
the amount of combustion air and fuel delivery are increased very
gradually. During the fuel oil pre-heating phase, voltage passes
through the regulation thermostat of the pre-heater and reaches
the relay coil of the resistance’s.
The relay closes and takes current to the resistance’s which, in turn,
heat the fuel contained in the pre-heater. The minimum thermostat
of the pre-heater closes when the temperature reaches the value at
which it has been set. The control box will be connected only when
the temperature in the pre-heater reaches the value at which it has
been set and causes the resistance’s to be disinserted (an opening
of the contact of the regulation thermostat); therefore, the fuel oil in
the pre-heater should be at maximum temperature.
The control box (cyclic relay) of the burner is therefore connected
by the regulation thermostat of the pre-heater when it excludes the
resistance’s by disinserting the relative relay. The cyclic relay control
box carries out the ignition programme by starting up the fan motor
in order to effect the pre-ventilation phase.
If the air pressure supplied by the fan is sufficient to cause the
intervention of the relative pressure switch, the pump motor will be
turned on immediately and will carry out a pre-circulation of hot oil
in the burner pipes.
Oil from the pump reaches the pre-heater, is heated to the correct
temperature and when it comes out it passes through a filter before
reaching the atomizer unit. The hot oil circulates in the atomizer unit
without coming out of the nozzle because the passages leading to
the outward and return nozzles are closed.
This closure is carried out by “closing pins” applied to the ends of
the rods. These “pins” are pressed against their seats by strong
springs which are situated at the opposite ends of the rods. The oil
circulates, comes out of the atomizer group return, goes through
the sump where the TRU thermostat is inserted and arrives at the
return pressure regulator; it passes through this and reaches the
pump return and from there is discharged into the return. Hot oil
circulation, as described above, is carried out at a pressure value
slightly higher (some bar) than the minimum pressure at which the
return pressure regulator has been set (10 ÷ 12 bar).
The duration time of the pre-ventilation and oil pre-circulation phase
is defined. This time can be extended (theoretically indefinitely)
because a special device in the electric circuit does not allow the
ignition programme to be carried out until the temperature of the
fuel in the nozzle return pipeline has reached the temperature at
which the TRU thermostat (thermostat on the nozzle return) has
been set. This special device does not allow the fuel to pass through
the nozzle until it has reached at least the temperature at which the
Control box &
relative Pro -
grammer
Safety
Time
in seconds
Pre-Ventilation & Oil Pre-
circulation Time
in seconds
Pre-ignition
Time
in seconds
Post-ignition
Time
in seconds
Time between
1st & 2nd flame
in seconds
LFL 1.333
Relè ciclico
3 31,5 6 3 12
CONTROL BOX SPECIFICATIONS
TRU thermostat has been set. Normally, intervention of the TRU
thermostat takes place within the pre-ventilation time; if it does
not, pre-ventilation and fuel oil pre-circulation are extended until
the intervention of the TRU thermostat.
The intervention of the TRU thermostat (oil in circulation sufficiently
hot) allows the control box to proceed with carrying out the ignition
programme by inserting the ignition transformer which in turn feeds
the electrodes with high voltage. High voltage between the electro -
des primes the electric spark for ignition of the fuel/air mixture. After
the insertion spark appears, the control box carries voltage to the
magnet, which by means of appropriate levers, moves backwards
the two rods which intercept the flow (outward and return) of fuel to
the nozzle. This moving backwards of the rods also determines a clo -
sing of the passage (by-pass) inside the atomizer unit. Consequently,
the pump pressure is taken to the normal value of about 20 ÷ 22
bar. Deviation of the two rods from the closing seat, now permits the
fuel to enter the nozzle at the pressure at which the pump has been
regulated at (20 ÷ 22 bar), and comes out of the nozzle adequately
atomized. The return pressure, which determines delivery to the
furnace, is regulated by the return pressure regulator.
The value of the ignition flow rate (minimum delivery) should be
about 10 ÷ 12 bar). The atomized fuel which comes out of the
nozzle is mixed with air supplied by the fan and is then ignited by
the spark of the electrodes. Flame presence is detected by the pho -
toresistant cell (UV). The programme proceeds and surpasses the
“shut down” position, disconnects the ignition, and then connects the
delivery regulating circuit (fuel/air). The servomotor which regulates
delivery (fuel/air) commends an increase in the delivery of fuel and
combustion air at the same time. The increase in fuel delivery is
determined by a disk with a varied profile which, by rotating, can
determine a greater compression of the return pressure regulator
spring and thus an increase in the pressure itself. When the return
pressure increases, there is also a corresponding increase in fuel
delivery. There should also be an adequate increase in combustion
air to meet the increase in fuel delivery.
Adjustment can be carried out a first regulation by operating the
screws which vary the profile of the command disk of the combu -
stion air regulator. Fuel and combustion air delivery both increase
at the same time until they reach maximum value (fuel pressure at
the return pressure regulator is equal to about 18 ÷ 20 bar if the
pressure at the pump is at the value of 20 ÷ 22 bar).
Fuel and combustion air delivery remain at maximum value until
the boiler temperature (pressure, if steam boiler), approaches the
value at which it has been set and causes the servomotor regulating
delivery (fuel/air) to reverse its previous sense of movement.
The return movement of the servomotor causes a reduction in fuel
delivery and a relative reduction in combustion air until they reach
minimum value. Should the maximum temperature (pressure, if
steam boiler) be reached even with fuel and combustion air delivery
at a minimum, the thermostat (pressure switch, if steam boiler) will