baltur GI Series Instruction page 31

DIFFERENTIAL AIR PRESSURE SWITCH WORKING
The air pressure switch works to ensure safe working of the equip-
ment (locking it off) if the air pressure is not at the expected level. The
pressure switch must therefore by adjusted to act by closing the NO
contact (normally open) when the air pressure in the burner reaches
a certain level. The connection circuit for the pressure switch is self-
controlling and so the NC contact (normally closed), which should
be closed when idle (with the fan off and therefore no air pressure
in the burner), must actually be in this state, if not the control and
command equipment will not go on (the burner stays off). If the NO is
not closed (normally open), where it should be closed when working,
(insufficient air pressure) the equipment carries out its cycle but will
not switch on the ignition transformer ignition and the gas pilot will
not go on, with the result that the burner locks off.
Adjustment before switching on the burner:
set the pressure switch at minimum.
Adjustment after burner calibration:
connect a manometer to the positive (+) pressure intake and another
manometer at the negative pressure (-) intake of the pressure switch.
Check at what point in the modulation there is the smallest pressure
difference (∆p) and adjust the pressure switch at the half-way point
of this difference.
Example: positive value + 1.5 mbar, negative value - 0.5 mbar
difference + 2 mbar, calibration 2:2 = 1 mbar
GAS PRESSURE SWITCH WORKING
The minimum and maximum gas pressure control switches have the
aim of preventing the burner from working when the gas pressure
goes outside the preset limits. The specific working of the pressure
switches naturally means that the minimum pressure control switch
uses the NO contact (normally open) so that it is closed when the
pressure switch detects a pressure greater than that set. Similarly
the maximum pressure switch uses the NC contact (normally closed)
so that it is closed when the pressure switch detects a pressure
below that set. The adjustment of the minimum and maximum gas
pressure switches must therefore take place when the burner is
being tested, according to the pressure found from time to time.
The pressure switches are connected up in such a way that the
triggering of any of these switches, (opening of the circuit), when
the burner is firing, will result in immediate burner shut-down.
Adjustment before switching on the burner: adjust the minimum
pressure switch at the scale's minimum and adjust the maximum
pressure switch at the scale's maximum.
Adjustment after burner calibration: With the burner at its
maximum output, adjust the minimum pressure switch by
increasing the calibration until the burner switches off, read
the calibration setting on the adjustment ring nut and set this
to 5 mbar less. With the burner off, adjust the maximum pres-
sure switch by reducing the calibration until the NC contact
(normally closed) opens. Read the value on the adjustment ring nut
and adjust this by increasing it by 5 mbar.
Note: the pressure switch will be for minimum pressure if there is
only one of these mounted on the gas train.
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