OPERATING CYCLE
Depending on the device to which the air valve operation servo control is interlocked, the burner can operate in
two different modes: gradual two-stage, if the control organ is of the on/off type, continuous flame modulation
if the device is of the modulating type.
GRADUAL TWO-STAGE OPERATION
2
stage
nd
1
stage
st
ignition
This is obtainable with standard open/close (on/off) boiler thermostat (or pressure switch) so by means of the
servo control, the air valve operates in two positions : minimum (1
We have gradual two-stage operation because change from one to the other takes place gradually and
smoothly.
a) Stop sequence: with the burner stopped, the air valve is in closed position to prevent the air from entering
and cooling the combustion chamber of the boiler and stack.
b) Preventilation sequence: the air valve is in fully open position with subsequent return to partially closed
position corresponding to the ignition capacity (with gas flow always closed).
c) Ignition flame formation sequence: the electronic gas coil is energized and the gas regulator is partially
open in relation to the pressure of the ignition air.
d) Main flame or second stage switchover sequence: the servo control commands opening of the air (up to
maximum setting capacity) and the increase in pressure causes a gradual increase in gas flow.
e) Maximum delivery to first stage switchover sequence: the boiler thermostat/pressure switch (regulator)
commands the servo control to close the air. The consequent pressure drop at the burner head causes the
gradual reduction of gas flow until minimum delivery is achieved. The burner repeats switchover from first to
second stage or from second to first stage and comes to a complete stop, always in relation to the command
given by the boiler regulator to the servo control.
CONTINUOUS MODULATION OPERATION
Ignition
min.30%
AIR
GAS
1 sec. max
operation
stage) or maximum opening (2
st
AIR
GAS
1 sec. max
Modular operation
37
time
stage).
nd
time
M
UK