baltur GI 350 ME Manual De Instrucciones página 35

DIFFERENTIAL AIR PRESSURE SWITCH WOR-
KING
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.
ADJUSTEMENT OF THE AIR FLOW TO THE BUR-
NER HEAD (see BT 8769/1)
The burner head is fitted with a regulator control, which closes or
open the air passage between the disk and the head. By closing the
air passage, a high pressure on the disk can be achieved, for low
rates as well. The increased speed and turbulence of the air makes
it penetrate with increased force, thus giving a better mixture and
greater flame stability. It may be essential to have high air pressure
at the disk, to stop flame pulsation.
This condition is practically indispensable when the burner is wor-
king on a pressurized boiler and/or a high thermic load. It is clear
from the above description that the device that closes the air to the
burner head must be taken to a position where it always obtains a
level behind the disk that is much higher than the air pressure level.
It is recommended to set the device with the air to the head
closed off, so that a sizable opening is required on the
air shutter that controls the flow to the burner fan intake.
Obviously, this condition must occur when the burner is working at
the maximum desidered delivery rate. In practice, the setting opera-
tion shuld be started with the device that closed the air to the burner
head at an intermediate position, and the burner should be started
up for a trial setting procedure, as described previously. When the
maximum desired delivery rate is reached, adjust the position of
the device that closes the air to the burner head, moving it forwards
or backwards in order to achieve an adequate air flow in delivery,
with the intake air control shutter well open. When reducing the size
of the air passage to the burner head, avoid closing it completely.
Ensure that the burner head is perfectly centered in relation to the
disk. If it is not perfectly centered, the flame may burn badly and
overheat the head, causing rapid deterioration. The centering can
be checked by looking from the inspection hole on the rear part
of the burner and then fully tightening the screws (if present) that
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