43 /
000608006_2007/06
DESCRIPTION OF OPERATIONS MODULATING
(see N° 0002906)
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 after the ignition flame (pilot)
valves and the safety valve 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” po
-
sition 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 8815).
The burner remains in the maximum delivery position until the temperature or pressure reaches the limit set for the
intervention of the modulation probe and makes the servomotor regulating gas/air delivery rotate in the opposite
sense of direction. Thus gas delivery and the relative combustion air are gradually reduced until they reach mini
-
mum level. Even 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 the programme previously described.
During normal operations, the boiler modulation probe fitted to the boiler detects the variations requested and
automatically proceeds with adapting the fuel and combustion air delivery by inserting the servomotor which re
-
gulates delivery (gas/air). This will rotate in such a way as to obtain an increase or a decrease.
With this manoeuvre, the gas/air delivery regulating system tries to equilibrate the quantity of heat supplied to the
boiler with that which the boiler gives to be utilized.
If the flame does not appear 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.
Safety time
in seconds
3
Pre-ventilation
time with shutter
open in seconds
3,5
Pre-ignition
in seconds
6
Post-ignition
in seconds
3
Time between 1st flame
& modulation start
in second
2
Control box &
relative
programmer
LFL .333
Cyclic relay
Summary of Contents for GI 350 DSPGN
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