baltur COMIST 122 DSPGM, Instruction

Page: 24 / 70

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DESCRIPTION OF MODULATING OPERATIONS WITH NATURAL GAS FOR COMIST....MM
(see N° 0002910610 and N° 0002910640)
CONTROL BOX SPECIFICATIONS
The field of variation in flow obtainable is from 1 to 1/3.
The burner is fitted with an end-of-the-run switch (a micro-switch) which stops the burner starting up if the flow
regulator is not in the minimum position. Before ignition, a pre-ventilation of the combustion chamber occurs (according
to Regulations) with air open. At the end of the ventilation phase, if the air ventilation pressure switch has measured
sufficient pressure, the ignition transformer will be connected and subsequently the ignition flame (pilot) valves and
the safety valves will open. Gas reaches the combustion head, mixes with air supplied by the fan, and is ignited.
Delivery is regulated by the flow regulator incorporated in the ignition flame (pilot) valve.
The ignition transformer is disconnected after the ignition flame and safety valves are inserted.
The burner is now operating with the ignition flame (pilot) only.
Flame presence is detected by a relative control device (ionization probe immersed in the flame, or UV cell).
The relay programmer passes the “shut down” position and gives voltage to the servomotor which regulates the
delivery (gas/air); the burner is now operating at minimum output. If the modulation probe allows it (regulated at a
temperature or pressure value superior to that existing in the boiler), the servomotor which regulates the gas/air
delivery starts turning and determines a gradual increase in the gas delivery and in the relative combustion air until
it reaches the maximum delivery value at which the burner has been regulated.
N.B. The “V” cam of the servomotor regulating gas/air delivery (see BT 8562/1) inserts almost immediately the
principle gas valve, which in turn opens completely. Gas delivery is not determined by the principle valve but
by the position of the gas delivery regulation valve (see BT 8816/1 and BT 8813/1).
The burner remains in the maximum delivery position until the temperature or pressure reaches the limit set for the
intervention of the modulation device (pressure switch or thermostat); the modulation motor will now rotate in the
opposite direction. The reverse rotation of the modulation motor causes a decrease in the fuel delivery and in the
relative combustion air. The reverse rotation and thus the reduction in delivery occur at brief intervals of time.
With this manoeuvre, the modulation system trys to equilibrate the quantity of heat supplied to the boiler with that
which the boiler gives to be utilized.
From this moment, the modulation device fitted to the boiler (thermostat or pressure switch) detects the variations
requested and automatically proceeds with adapting the fuel and combustion air delivery by inserting the modulation
motor, which will rotate in such a way as to obtain an increase or s decrease.
With delivery at a minimum, if the limit (temperature or pressure) at which the shut down device (thermostat or
pressure switch) has been regulated is reached; the burner will be brought to a standstill.
When the temperature or pressure drops below the intervention limit set on the shut down device, the burner will
start up again according to its programme, as previously described.
Note: If the flame does not appear within two seconds from the opening of the first flame valves (pilot), the control
box goes to “shut down” (the burner stops completely and the relative indicator light is turned on).
To unblock the control box, press the appropriate pushbutton.
Control box
&
relative
programmer
LFL 1:333
Cyclic relay
Safety time
in seconds
3
Pre-ventilation
time with
shutter open
in seconds
31,5
Pre-ignition
in seconds
6
Post-ignition
in seconds
3
Time between
1st flame &
modulation start
in seconds
12