Service manual

16
97-05
BOILER GUN BURNER
CELLA
GAS INSTALLATIONS WITH AIR BLOWN BURNERS
The gas circuit is made up of the following components:
• a “TANDEM” gas solenoid valve unit consisting of:
- a safety solenoid valve which remains open during the
entire operating time;
- a second solenoid valve (normally closed) which only
opens when a heating command is received, thus allowing
the passage of the gas to the burners;
- a third device which permits the partial closing of the gas
solenoid valve in order to reduce the gas flow during
operation, thus reducing the power to 70% with respect to
the nominal operating capacity. This device is only acti-
vated during cooking cycles using reduced power.
• a heat exchange burner
• a heat exchanger. The oven chamber heat exchanger
consists of a spiral shaped corrugated tube which wraps
around the oven chamber ventilator fan. The heat ex-
changer is connected at one end to the to the burner and the
other end opens directly in to the ambient atmosphere;
• a ventilator fan for the air blown burner;
• an air pressure switch which guarantees the correct
pressure inside the burner before allowing ignition;
• one or two spark plugs and flame detection devices;
• a gas pressure switch which cuts off the gas flow in case
of insufficient pressure. This intervention is indicated by the
oven chamber light switching off;
• an electronic ignition and flame control device (control-
ler).
IGNITING THE BURNER
When a cooking cycle is started the flame control device is
activated which in turn activates the heating circuit in
various stages as follows:
1) Air pressure switch check
The controller sends an impulse to the air pressure switch
which has normally open contacts. If the circuit is functional
the ventilation stage is activated. If the pressure switch
circuit is damage neither the ventilation nor the ignition
stages are activated.
2) Ventilation stage
The controller activates the ventilator fan which after a few
seconds activates the pressure switch moving it’s contacts
from open to closed and this in turn allows the wash stage
to begin. If the circuit isn’t functioning due to ventilator or
pressure switch failure the controller will continue to allow
the ventilators to work without moving on to the successive
stage.
3) Wash stage
The ventilator lets air into the heat exchanger for about 10
seconds in order to realise the correct pressure and at the
same time eliminate any eventual traces of gas or fumes.
At the end of the wash stage the controller allows the
ignition stage to begin.
4) Ignition stage
Ten seconds after the wash stage has started the controller
simultaneously enables the ignition of the spark plug (by
sending a 15,000V charge) allows gas to be fed to the valve
and activates the flame detector. A this point two situations
are possible:
a) The flame ignites correctly and is detected. This is the
normal functioning condition which is followed by maintain-
ing continuous combustion at the burner, by the flame
detection and consequent spark plug disactivation (once
ignition has taken place the charge at the spark plug is
reduced to 200V)
b) The flame does not light up, or it lights up but is not
detected. In this case the controller will continue to supply
the gas valve and activate the ignition and detection
devices for a safety period of 5 seconds.
If during this period the flame does not light or is still not
detected the controller will switch everything off and acti-
vate the burner block condition which is indicated by the
lighting up of the luminous buttons “EC” or “RB” (oven
chamber reset or boiler reset). At this point, and after having
eliminated the cause of the blockage (see chapter “trouble
shooting”, pressing the reset button “RC” or “RB” will force
the controller to start again from point 1.
Note: Should the spark plugs be replaced it is extremely
important that they be positioned as shown in figures 11a
for the boiler and 11b for the oven chamber.
Fig.13a
Fig.13b
COOKING CHAMBER GUN BURNER
V
A
B
3Ö4mm
B
A
V
3Ö4mm