baltur BT 75 DSPN-D Mode D'emploi page 38

The servomotor which regulates delivery (fuel/air) commends an increase in the delivery of fuel and combustion
air at the same time. The increase in fuel delivery is determined by a disk with a varied profile which, by rotating,
can determine a greater compression of the return pressure regulator spring and thus an increase in the pressure
itself. When the return pressure increases, there is also a corresponding increase in fuel delivery.
There should also be an adequate increase in combustion air to meet the increase in fuel delivery.
Adjustment can be carried out at first regulation by operating the screws which vary the profile of the command
disk of the combustion air regulator. Fuel and combustion air delivery both increase at the same time until they
reach maximum value (fuel pressure at the return pressure regulator is equal to about 18 ÷ 20 bar if the pressure
at the pump is at the value of 20 ÷ 22 bar).
Fuel and combustion air delivery remain at maximum value until the boiler temperature (pressure, if steam boiler),
approaches the value at which it has been set and causes the servomotor regulating delivery (fuel/air) to reverse
its previous sense of movement. The return movement of the servomotor causes a reduction in fuel delivery and
a relative reduction in combustion air until they reach minimum value.
Should the maximum temperature (pressure, if steam boiler) be reached even with fuel and combustion air
delivery at a minimum, the thermostat (pressure, if steam boiler) will intervene when the value at which it has been
set is reached, and bring the burner to a standstill. When the temperature (pressure, if steam boiler) drops below
the intervention limit of the "shut down" device, the burner will start up again as previously described.
During normal operations, the thermostat (or pressure switch) of the 2nd stage is aware of load variations in the
boiler and automatically requests the servomotor regulating delivery (fuel/air) to make an adjustment in the fuel
delivery and in the relative combustion air. With this manoeuvre, the delivery regulating system (fuel/air) reaches
a position of equilibrium which corresponds to a fuel delivery and a relative combustion air delivery equal to the
quantity of heat required by the boiler. It should be kept in mind that the field of variation in output obtainable with
a good combustion is, as an indication, from 1 to 1/3 of the maximum output given on the rating plate.
Note: The air pressure switch must be set when the burner is started up and must be in function with the pressure
value verified during operation with the ignition flame.
DESCRIPTION OF MODULATING OPERATION (BT...MNM) (See BT 8712/3)
While fuel oil is being pre-heated, voltage passes through the pre-heater regulation thermostat and reaches the
coil of the elements remote-switch.
This remote-switch is cut-in and takes current to the pre-heater elements which heat the fuel inside the pre-
heater.
The elements that heat the pump and atomizer unit (only for the ...D version) are also cut-in through panel
switch ( I ). The minimum level thermostat for the pre-heater is cut-in when temperature reaches the level to which
it is set. The equipment is cut-in only when the temperature at which elements are cut-off is reached in the pre-
heater (the thermostat regulation contact opens). This means fuel oil in the pre-heater must be at maximum
temperature. The burner command/control equipment (cyclic relay) is therefore cut-in by the pre-heater regulation
thermostat when the latter cuts-off the elements by switching off the relative remote-switch.
Control box Safety Time
& relative in seconds
Programmer
LAL 1.25
Cyclic relay
Control box specifications
Pre-Ventilation & Oil
Pre-circulation Time
in seconds
5 22,5
Pre-ignition Time Post-ignition
in seconds
2,5
38
Time between
Time 1st flame & Start
in seconds of Modulation
in seconds
20
5