baltur COMIST 122 DSPGM, Инструкция

Страница: 19 / 70

19
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”.
DESCRIPTION OF MODULATING OPERATIONS WITH LIGHT OIL (COMIST...MM)
(See BT 8714/2)
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) +
- pre-ventilation 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.
Safety Time
in seconds
3
Pre-Ventilation &
Oil Pre-circulation
Time
in seconds
31,5
Pre-ignition
Time
in seconds
6
Post-ignition
Time
in seconds
3
Time between
1st flame & Start
of Modulation
in seconds
12
Control box
& relative
Programmer
LFL 1.333
Cyclic relay