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5.7.4
Low oil pressure switch
The low oil pressure switch is factory set to 261 PSI (18 bar). If the
oil pressure goes down this value in the delivery piping, the pres-
sure switch stops the burner. Burner starts again automatically if
the pressure goes above 261 PSI (18 bar) after burner start up.
5.7.5
High oil pressure switch
The high oil pressure switch is factory set to 43.5 PSI (3 bar). If the
oil pressure goes above this value in the return piping, the pressure
switch stops the burner. Burner starts again automatically if the
pressure goes down under 43.5 PSI (3 bar) after burner shut down.
If a loop circuit with Px pressure feeds the burner, the pressure
switch should be adjusted to Px + 43.5 PSI. For the adjustment,
see (Fig. 50).
5.8
Burner starting (fuel oil adjustment)
Operating control closes, the motor starts.
The pump 3)(Fig. 51) draws the fuel from the tank through the
piping 1) and pumps it under pressure for delivery.
The piston 4) rises and the fuel returns to the tank through the
piping 5) - 7).
The screw 6) closes the by-pass heading towards suction and
the de-energized solenoid valves 8) - 9) - 2) close the passage
to the nozzle.
Air damper and pressure regulator are positioned on MIN out-
put.
Ignition electrode strikes a spark.
Solenoid valves 8) - 9) - 2) open; the fuel passes through the
piping 10) and filter 11), and enters the nozzle.
A part of the fuel is then sprayed out through the nozzle, ignit-
ing when it comes into contact with the spark: flame at a low
output level; the rest of the fuel passes through piping 12 at
the pressure adjusted by the regulator 13, then, through piping
7), it goes back into the tank.
The spark goes out.
The starting cycle ends.
5.8.1
Steady state operation
At the end of the starting cycle, the servo-motor control then pass-
es to load control for boiler pressure or temperature.
If the temperature or pressure is low (and the load control is
consequently closed), the burner progressively increases out-
put up to MAX.
If subsequently the temperature or pressure increases until
the load control opens, the burner progressively decreases
output down to MIN.
The burner shuts off when demand for heat is less than the
heat supplied by the burner in the MIN output.
The servomotor returns to the 0° angle limited by contact with
cam 2. The air damper closes completely to reduce thermal
dispersion to a minimum.
Every time output is changed, the servomotor automatically modi-
fies oil delivery (pressure regulator) and air delivery (fan damper).
20036932
Start-up, calibration and operation of the burner
36
+
D10627
D10157
5.8.2
Firing failure
If the burner does not fire, it goes into lock-out within 3 sec. of
the opening of the light oil valve.
If the flame should go out for accidental reasons during opera-
tion, the burner will lock out in 1 s.
GB
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Fig. 50
Fig. 51
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