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Idiomas disponibles
DESCRIPTION OF TWO STAGE PROGRESSIVE
OPERATION (BT...DSPN) (See BT
We refer to a two-stage progressive operation because the passage
from the 1st flame to the 2nd flame (from the minimum rate to the
maximum pre-established rate) takes 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 resistances.
The relay closes and takes current to the resistances which, in
turn, heat the fuel contained in the pre-heater.
The minimum thermostat of the pre-heater closes when the tem-
perature 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 resistan-
ces 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
resistances 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-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 22,5 seconds.
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
TRU thermostat has been set. Normally, intervention of the TRU
thermostat takes place within the pre-ventilation time 22,5 seconds);
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
8712/3)
with high voltage. High voltage between the electrodes primes the
electric spark for ignition of the fuel/air mixture. 5 seconds after
the ignition 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 closing of the passage (by-pass) inside the atomizer unit. Con-
sequently, 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 photoresistant. The programme
proceeds and, after 5 seconds, 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 at 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 regula-
ting 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, if steam boiler) will intervene when the
value at which it has been set is reached, and bring the burner to
a standstill. When the temperature (pressure, if steam boiler) drops
below the intervention limit of the "shut down" device, the burner
will start up again as previously described.
During normal operations, the thermostat (or pressure switch)
of the 2nd stage is aware of load variations in the boiler and
automatically requests the servomotor regulating delivery (fuel/
air) to make an adjustment in the fuel delivery and in the relative
combustion air. With this manoeuvre, the delivery regulating system
(fuel/air) reaches a position of equilibrium which corresponds to
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