- 37
-
ENGLISH
OPERATING CYCLE
Depending on the device with which air gate operation servo control is interlocked, the burner can operate in two different
modes:
gradual two-stage
, if the control unit is of the on/off type,
continuous
fl
ame modulation
if the device is of the
modulating type.
GRADUAL TWO-STAGE MODE
This is obtainable with a standard open/close (on/off) boiler thermostat (or pressure switch) so by means of the servo control,
the air gate operates in two positions: minimum (1st stage) or maximum opening (2nd stage).
We have gradual two-stage operation because the change from one to the other takes place gradually and smoothly.
From the illustrated diagram, the following characteristic sequences can be seen:
a) Stop sequence:
with the burner stopped, the air gate is in closed position to prevent the air from entering and cooling
the combustion chamber of the boiler and
fl
ue.
b) Preventilation sequence:
the air gate is in the fully open position with subsequent return to partially closed position
corresponding to the ignition delivery (with gas
fl
ow always closed).
c) Ignition
fl
ame formation sequence:
the electronic gas valve coils are energized and the gas regulator is partially open
according to the pressure of the ignition air.
d) Main
fl
ame or second stage switchover sequence:
the servo control commands opening of the air (up to maximum
delivery setting) and the increase in pressure causes a gradual increase in gas
fl
ow.
e) Maximum delivery to
fi
rst stage switchover sequence:
the boiler thermostat/pressure switch (regulator) acts on the
servo control thus closing the air.
CONTINUOUS MODULATION MODE
This mode is obtained by sending an appropriate signal to the air gate servo control so that power supplied by the burner
can be of any intermediate value between a preset minimum and maximum. Continuous modulation is required when boiler
water temperature or steam pressure must be kept within restricted limits. From the diagram, it will be seen that the stop,
preventilation,
fl
ame formation or switchover to maximum output phases are the same as those described in the previous
paragraph. Actual
fl
ame modulation is obtained by
fi
tting the following devices to the system. These are supplied with an
optional kit:
-
LANDIS boiler probe,
for temperature or pressure.
-
LANDIS RWF 32 regulator
with mounted case panel.
-
Range adapter for regulator
, controlled by the boiler probe, with calibration suitable
for the probe scale.
2˚stadio
avviam.
e
d
c
b
ARIA
GAS
a
a
0
1 sec. max
tempo
1˚stadio
operation
Modulation mode
time
AIR
ignition
min. ignition 30%
time
AIR
1st stage
ignition
2nd stage
