baltur COMIST 122 DSPGM Instruction Download

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DESCRIPTION OF TWO STAGE PROGRESSIVE OPERATIONS WITH LIGHT OIL
COMIST...DSPGM

(See BT 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 ).

Control box specifications

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 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 unit return and 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 pressure 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 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) +
- preventilation time foreseen by the control box +
- the closing stroke of the delivery regulation servomotor (fuel/air) until ignition air position.
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. 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 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 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 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 photocell UV.
The programme proceeds and 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.