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5.5
Final adjustment of the pressure switches
5.5.1
Air pressure switch
Adjust the air pressure switch (Fig. 28) after performing all other
burner adjustments with the air pressure switch set to the start of
the scale.
With the burner operating at minimum output, insert a combus-
tion analyser in the stack, slowly close the suction inlet of the fan
(for example, with a piece of cardboard) until the CO value does
not exceed 100 ppm.
Slowly turn the appropriate knob clockwise until the burner goes
into lockout.
Check the indication of the arrow pointing upwards on the gradu-
ated scale. Turn the knob clockwise again, until the value shown
on the graduated scale corresponds with the arrow pointing
downwards, and so recovering the hysteresis of the pressure
switch (shown by the white mark on a blue background, between
the two arrows).
Now check the correct start-up of the burner. If the burner locks
out again, turn the knob anti-clockwise a little bit more. During
these operations it may be useful to measure the air pressure
with a pressure gauge.
The connection of the pressure gauge is shown in Fig. 28. The
standard configuration is that with the air pressure switch con-
nected in absolute mode. Note the presence of a "T" connection,
not supplied.
In certain applications in strong depression situations, the con-
nection of the pressure switch does not allow it to change over.
In this case it is necessary to connect the pressure switch in dif-
ferential mode, applying a second tube between the air pressure
switch and the fan suction line mouth.
In this case also, the pressure gauge must be connected in differ-
ential mode, as shown in Fig. 28.
5.5.2
Maximum gas pressure switch
Adjust the maximum gas pressure switch (Fig. 29) 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.
Start-up, calibration and operation of the burner
Connection of the pressure gauge
with the pressure switch in abso-
lute mode
D3856
33
GB
D3951
20198301
PA
PGM
-
+
Fig. 28
20181543
Fig. 29
20205048
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