20160778
26
GB
Installation
4.15 Burner operation
4.15.1 Burner starting
•
Operating closes.
Fan motor starts (A Fig. 30).
•
Servomotor starts:
130° rotation to right, until contact is made on red cam.
The air damper is positioned to MAX. output.
•
Pre-purge stage with air delivery at MAX. output.
•
After pre-purge stage, servomotor rotates to left up to the angle
set on black cam for MIN. output.
•
The air damper and the gas butterfly are positioned to MIN. out-
put.
•
Ignition electrode strikes a spark.
•
Pilot valve opens. The pilot flame is ignited.
•
After about 12s the main flame ignites and after 10s there is the
consent to modulation and the servomotor reads the input sig-
nal and starting cycle ends.
4.15.2 Steady state operation
Burner with external control signal
At the end of the starting cycle, the servomotor control then passes
to the load control for boiler pressure or temperature.
By three types of input signals:
– 4-20 mA
– 2-10V
– 0-135 ohm
(The flame safeguard continues, however, to check that the flame
is present and that the air pressure switch is in the correct position.)
•
If the input signals is high, the burner progressively increases
its output to the MAX. value.
•
If the input signals is low, the burner progressively decreases
its output to the MIN. value. And so on.
•
The burner locks out when demand for heat is less than the
heat supplied by the burner at min. output. Load control opens.
The servomotor returns to the 0° angle limited by contact with
orange cam. The air damper closes completely to reduce ther-
mal dispersion to a minimum.
Every time output is changed, the servomotor automatically modi-
fies gas delivery (gas butterfly valve) and air delivery (fan damper).
Tab. H
Key for the times
t1
Pre-purge time with air damper open
t2
First safety time
t3
Pre-ignition time, short (ignition transformer on terminal 16)
t4
Interval between main fuel piloted valve and release to modu-
lation
t5
Running time of air damper into OPEN position
t6
Running time of air damper into low-flame position (MIN)
t7
Post-purge time
t8
Interval until OPEN command for the air damper is given
t9
Running time of pilot
T10
Second safety time
TL
Operating control
MV
Fan Motor
SM
Air and Fuel Actuator
TA
Ignition transformer
VP1
Safety pilot valve
VP2
Main pilot valve
V1
Safety gas valve
V2
Main gas valve
4.15.3 Firing failure
If the burner does not fire, it locks out within 2.5 seconds from
opening the pilot valve and then within 5 seconds from opening
the main valves.
4.15.4 Burner flame goes out during operation
If the flame should accidentally go out during operation, the burner
will lock out within 1s.
RFGO A13
t1
t2
t3
t4
t5
30s
4.2s
2s
10s
36s
t6
t7
t8
t9
t10
31s
12s
4s
17s
4.2s
Fig. 30
FULL MODULATION
20162566
GAS BUTTERFLY
AIR DAMPER
External Signals
