Baltur GI 1000 DSPG Instructions For Use Manual - page 37
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0006080767_201002
DESCRIPTION OF TWO STAGE PROGRESSIVE
OPERATIONS
(See BT 8714/2)
This is referred to as a 2-stage progressive operation because the
passagefromthe1stflametothe2ndflame(fromtheminimumrate
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.
Itisnecessarythattheairpressuresuppliedbythefanissufficient
to cause the intervention of the relative pressure switch, if not, the
control box will go to “shut down”.
Oilfromthepumpreachestheatomizerunitandcirculateswithin
itbecausethepassagesleadingtotheoutwardandreturnnozzles
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.Theoilcirculates,comesoutoftheatomizerunitreturnand
arrives at the return pressure regulator.
It passes through this and reaches the pump return and from there
it is discharged back into the return.
Oil circulation, as described above, should be carried out at a pres-
sure value slightly higher (by some bar) than the minimum pressure
at which the return pressure regulator has been set (10 ÷ 12 bar).
Duration of the pre-ventilation and oil pre-circulation phase is not
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
backwardsthetworodswhichintercepttheflow(outwardandreturn)
oflightoiltothenozzle.Thismovingbackwardsoftherodsalso
determinesaclosingofthepassage(by-pass)insidetheatomizer
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
toenterthenozzleatthepressureatwhichthepumphasbeen
regulatedat(20÷22bar),andcomesoutofthenozzleadequately
atomized.
The return pressure, which determines delivery to the furnace, is
regulated by the return pressure regulator.
Thevalueoftheignitionflowrate(minimumdelivery)shouldbe
about 10 ÷ 12 bar.
Theatomizedlightoilwhichcomesoutofthenozzleismixed
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
isdeterminedbyadiskwithavariedprofilewhich,byrotating,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.
Adjustmentcanbecarriedoutatfirstregulationbyoperatingthe
screwswhichvarytheprofileofthecommenddiskofthecombu-
stion 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 tem-
perature 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
boilerthermostat/pressureswitchofthe2ndstagefittedtothe
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
bytheboiler.Asinindication,itshouldbekeptinmindthatthefield
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
valueverifiedduringoperationswiththeignitionflame;
otherwise the control box will go to “shut down”.