baltur GI MIST 1000 DSPGM Instruction Manual page 57

Just 2.5 seconds after the ignition of the pilot flame, the control box
powers the magnet which, via a series of lever mechanisms, moves
the two nozzle fuel flow (delivery and return) interception rods.
When the rods move back they close the atomization unit internal
passage (by-pass) bringing the pump pressure to the standard value
of approx. 18 ÷ 20 bar.
The movement of the two rods from the closure seats makes it
possible for the fuel to enter the nozzle at the pump pressure of
20 ÷ 22 bar, and exit from the nozzle in a suitable atomized status.
The return pressure, which determines delivery to the furnace, is
regulated by the return pressure regulator.
For the ignition flow rate (minimum output) this value is approx.
10 - 12 bar. The atomised fuel which exits the nozzle mixes with
the fan-fed air and is ignited by the already-lit gas pilot flame. After
the magnet is switched on the pilot flame is switched off and the
burner is run at the modulation minimum. Flow increase occurs
automatically and continuously according to the signals from the
modulation probe fitted to the boiler, and is carried out by means
of a servomotor. The modulation motor controls the increase of the
contemporary output of fuel and combustion air. The increase in
the flow of fuel is determined by the variable-profile disk which, by
rotating, causes greater compression of the return pressure regulator
spring and thus an increase in return pressure corresponds to an
increase in fuel flow. An increase in fuel delivery must correspond
to an increase (of adequate quantity) of combustion air.
This condition is created during the first regulation, by turning the
screws that vary the profile of the control disc that regulates the
combustion air.
Fuel flow and, at the same time, combustion air flow, increase up
to maximum pressure (fuel pressure at return pressure regulator
of about 18 - 20 bar) if pressure at the pump is 20 - 22 bar. Fuel
and combustion air delivery rates remain at maximum until boiler
temperature (pressure in the case of a steam boiler)approaches the
set value and causes the modulation control motor to invert rotation.
The return movement of the modulation motor causes a reduction
in the delivery of fuel and relative combustion air. The modulation
system reaches a position of equilibrium which corresponds to a
delivery of fuel and relative combustion air equal to the quantity of
heat requested by the boiler.
With the burner working the in-boiler probe detects variations in
boiler load and automatically sends a signal to the modulation motor
to adjust the flow of fuel and relative combustion air accordingly.
If, even with just the minimum flow of fuel and combustion air,
the maximum temperature (or pressure in the case of a steam
boiler) is reached, the thermostat (pressure switch in the case of a
steam boiler) will shut down the burner completely. Subsequently,
the temperature (or pressure in the case of a steam boiler) will
drop below the shut-down setting and the burner will re-ignite as
described above. Bear in mind that the possible flow range, with
good combustion, is approximately from 1 to 1/3 of the max flow rate
indicated on the ID plate. Should the flame fail to appear within two
seconds of the pilot flame igniting, the control box places the unit in
"lock-out" (complete shutdown of burner with relative warning light).
To "resume" the equipment operation press the dedicated button.
The air pressure switch must be adjusted on igniting the
burner as a function of the pressure value observed for
operation with the pilot flame.
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