20160778
30
GB
Start-up, calibration and operation of the burner
5.6
Final calibration of the pressure switches
5.6.1
Air pressure switch
Adjust the air pressure switch after having performed all other burn-
er adjustments with the air pressure switch set to the start of the
scale (Fig. 39).
With the burner operating at minimum output, increase adjustment
pressure by slowly turning the relative dial clockwise until the burn-
er locks out.
Then turn the dial anti-clockwise by about 20% of the set point and
repeat burner starting to ensure it is correct.
If the burner locks out again, turn the dial anti-clockwise a little bit
more.
During these operations it may be useful to measure the air pres-
sure with a pressure gauge.
The connection of the pressure gauge is shown in Fig. 40.
The standard configuration is that with the air pressure switch con-
nected in absolute mode.
Note the presence of a “T” connection, not supplied.
The air pressure switch may operate in "differential" operation in
two pipe system.
If a negative pressure in the combustion chamber during pre-purg-
ing prevents the air pressure switch from switching, switching may
be obtained by fitting a second pipe between the air pressure
switch and the suction inlet of the fan. In such a manner the air
pressure switch operates as differential pressure switch.
5.6.2
Maximum gas pressure switch
Adjust the maximum gas pressure switch (Fig. 41) after making all
other burner adjustments with the maximum gas pressure switch
set to the end of the scale.
To calibrate the maximum gas pressure switch, open the tap and
then connect a pressure gauge to its pressure test point.
The maximum gas pressure switch must be regulated to a value no
higher than 30% of the measurement read on the gauge when the
burner is working at maximum output.
After making the adjustment, remove the pressure gauge and close
the tap.
5.6.3
Minimum gas pressure switch
The purpose of the minimum gas pressure switch is to prevent the
burner from operating in an unsuitable way due to too low gas pres-
sure.
Adjust the minimum gas pressure switch (Fig. 42) after having ad-
justed the burner, the gas valves and the gas train stabiliser. With
the burner operating at maximum output:
–
install a pressure gauge downstream of the gas train stabiliser
(for example at the gas pressure test point on the burner com-
bustion head);
–
choke slowly the manual gas cock until the pressure gauge de-
tects a decrease in the pressure read of about 0.1 kPa
(1 mbar). In this phase, verify the CO value which must always
be less than 100 mg/kWh (93 ppm).
–
Increase the adjustment of the gas pressure switch until it inter-
venes, causing the burner shutdown;
–
remove the pressure gauge and close the cock of the gas pres-
sure test point used for the measurement;
–
open completely the manual gas cock.
WARNING
1 kPa = 10 mbar
Fig. 39
D3854
Fig. 40
20161112
PGM
PA
D3856
20181543
Fig. 41
Fig. 42
D9290
