Publicité
3
FEATURES
3.1
ELECTRONIC
IGNITION
"RS Mk II" boilers have automatic ignition
(with no pilot light), so they have an SM 191.1
electronic control and protection device with
a built-in transformer (fig. 15).
Ignition and flame detection are controlled
by two sensors at the ends of the burner.
Ignition takes place directly in the burner;
the utmost safety is guaranteed, with trip-
ping times of within 2 seconds in the event
that the flame accidentally goes out or there
is no gas supply.
3.1.1
Functioning cycle
Before turning on the boiler use a volt meter
to check that the terminal board has been
wired up correctly, complying with the phase
and neutral positions shown in the diagram.
Press the switch on the control panel. At
this point the boiler will start up, sending
a current discharge through the SM191.1
programmer to the ignition electrode while
opening the gas valve.
When the gas pressure is insufficient, the
pressure switch does not enable the start-
up cycle and the insufficient gas pressure
warning signal is enabled. Burner ignition
normally takes 1 to 2 seconds.
In the event that ignition fails, the boiler
shutdown signal will be triggered. Let us
sum up how this can happen:
– Air in the gas pipes
The boiler performs the cycle normally,
sending voltage to the ignition electrode,
which continues to discharge for a maxi-
mum of 8 seconds. If the burner is not
ignited, the boiler shuts down.
This may occur the first time the boiler is
started up or when it has been inactive for
some time and there is air in the pipes. It
may be caused by failure to open the gas
valve due to an interruption in the electri-
cal coil.
– Ignition electrode fails to
discharge
The gas valve to the burner normally
opens; if this does not occur within 8
seconds the boiler will shut down.
This may be the result of an interruption
in the electrode cable, or the cable may
not be properly fastened to terminal 10;
or the boiler's transformer may have been
burnt out.
– The flame is not detected
The electrode continues to discharge even
though the burner is already ignited. After
about 8 seconds the discharge will stop
and the burner will be shut down, while
the device's shutdown indicator light will
come on.
This occurs if phase and neutral have not
54
2
4
PRIMA - SECONDA
FIRST-SECOND
ELETTROVALVOLA
GAS SOLENOID
GAS
VALVE
KEY
1 SM 191.1 device
2 Interference filter
be connected properly on the terminal
board. The detection electrode cable may
be interrupted or the electrode itself may be
grounded; the electrode may be worn and
require replacement.
NOTE: if the device shuts down, press the
illuminated pushbutton only after waiting
at least 20 seconds from when the indica-
tor light came on, or the device will not be
released.
3.1.2
Ionisation circuit
The ionisation circuit may be controlled
using a micro-ammeter with a dial or, bet-
ter yet, a digital reading, with a scale of 0
to 50 µ.
The micro-ammeter's terminals must be
wired up to the detection electrode cable
in series.
During regular operation the reading fluctua-
tes around 6÷12 µ . The minimum ionisation
current at which the device may be shut down
is around 1 µ .
If this occurs, check that there is proper electri-
cal contact and check the end of the electrode
and its ceramic guard for wear.
3
MINIMUM GAS
PRESSOSTATO
PRESSURE VALVE
GAS DI MINIMA
MINIMUM GAS
VALVOLA GAS
PRESSURE SWITCH
DI MINIMA
3 Ignition electrode
4 Detection electrode
3.2
STEP REGULATION THERMOSTAT
The "RS Mk II" boilers are equipped with a
regulation thermostat with double contact with
differentiated calibration which allows obtai-
ning, before the burner is completely switched
off, a power reduction through the 2nd stage
control (fig. 19).
This step modulation system allows you to
obtain the following advantages:
- a higher overall efficiency of the boiler.
- contain within acceptable values the increase
in temperature that occurs in the cast iron body
(thermal inertia) when the burner is turned off
3.3
OPPOSED INSTALLATION
OF TWO BOILERS
On request, accessories may be supplied to
permit opposed installation of two boilers so
as to reduce overall dimensions and permit
easy connection with the flue by allowing
flue gases to be evacuated through a single
duct (fig. 16-17).
Table 2 shows the dimensions of the two
combined boilers and stack diameter.
1
Fig. 15
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