baltur GI 350 DSPG Manual De Instrucciones página 36

DESCRIPTION OF TWO STAGE PROGRESSIVE
OPERATIONS
(See 8714/2)
This is referred to as a 2-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 place gradually both
as delivery of combustion air and of fuel. The burner's control box
(cyclic relay) is connected by operating panel switch ( I ).
The cyclic relay control box carries out the ignition programme by
starting up the fan motor and thus the pump in order to effect the
pre-ventilation and light oil pre-circulation phases.
It is necessary that the air pressure supplied by the fan is sufficient
to cause the intervention of the relative pressure switch, if not, the
control box will go to "shut down".
Oil from the pump reaches the atomizer unit and circulates within
it because the passages leading to the outward and return nozzles
are closed. This closure is carried out by "closing pins" applied to
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the ends of the rods.
These "pins" are pressed against their seats by strong springs which
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are situated at the opposite ends of the rods.
The oil circulates, comes out of the atomizer unit return and arrives
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at the return pressure regulator.
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It passes through this and reaches the pump return and from there
it is discharged back into the return.
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Oil circulation, as described above, should be carried out at a pres-
sure value slightly higher (by some bar) than the minimum pressure
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at which the return pressure regulator has been set (10 ÷ 12 bar).
Duration of the pre-ventilation and oil pre-circulation phase is not
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22,5 seconds, as foreseen by the control box, because it is effected
when the air shutter is in an open position.
The pre-ventilation and pre-circulation time is calculated by summing
together the times of the following manoeuvres:
- the delivery regulation servomotor's opening stroke (fuel/air) (45
seconds) +
- preventilation time foreseen by the control box (22,5 seconds) +
- the closing stroke of the delivery regulation servomotor (fuel/air)
until ignition air position (about 40 seconds).
Therefore, altogether, the duration of the pre-ventilation and oil
pre-circulation phase is about 107,5 seconds.
Subsequently, the control box continues carrying out the ignition
programme by connecting the ignition transformer which feeds the
electrodes with high voltage. The voltage between the electrodes
primes the electric spark for ignition of the fuel/air mixture. 2,5
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 light oil to the nozzle.
This moving backwards of the rods also determines a closing 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 the closing seat, now permits the fuel to en-
ter 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 light oil 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 cell.
The programme proceeds and, after 5 seconds, surpasses the
"shut down" position, disconnects the ignition transformer and by
this point on the burner is operating at minimum output. If the boiler
thermostat (or pressure switch) of the 2nd stage allows it (regulated
at a temperature or pressure value superior to that existing in the
boiler), the servomotor which regulates the delivery starts turning
and determines a gradual increase in the fuel delivery and in the
relative combustion air until it reaches the maximum delivery value
at which the burner has been regulated.
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 commend disk of the combustion
air regulator. Fuel and combustion air delivery both increase at the
same time until they reach maximum value (light oil 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). The burner remains in
the maximum delivery position until the temperature or pressure
reaches the limit set for the intervention of the boiler thermostat
(or pressure switch) of the 2nd stage and makes the servomotor
regulating fuel/air delivery rotate in the opposite sense of direction,
a causing gradual 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 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 boiler thermostat / pressure switch
of the 2nd stage fitted to the boiler detects the variations requested
and automatically proceeds with adapting the fuel and combustion
air delivery by inserting the servomotor which regulates delivery
(fuel/air). This will rotate in such a way as to obtain an increase
or a decrease. In this way, the delivery regulating system (fuel/air)
reaches a position of equilibrium which corresponds to a fuel delivery
and a relative combustion air delivery equal to the quantity of heat
required by the boiler.
As in indication, it should be kept in mind that the field of variation
in output obtainable with good combustion is from 1 to 1/3 of the
maximum output given on the rating plate.
Note: The air pressure switch must be set when the burner is
started up and must be in function with the pressure value
verified during operations with the ignition flame; otherwise
the control box will go to "shut down".
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