baltur BT 75 DSPN-D Mode D'emploi page 37

DESCRIPTION OF TWO STAGE PROGRESSIVE OPERATION (BT...DSPN) (See BT 8712/2)
We refer to a two-stage progressive operation because the passage from the 1st flame to the 2nd flame (from the
minimum rate to the maximum pre-established rate) takes gradually and therefore the amount of combustion air
and fuel delivery are increased very gradually.
During the fuel oil pre-heating phase, voltage passes through the regulation thermostat of the pre-heater and
reaches the relay coil of the resistances.
The relay closes and takes current to the resistances which, in turn, heat the fuel contained in the pre-heater.
The minimum thermostat of the pre-heater closes when the temperature reaches the value at which it has been
set. The control box will be connected only when the temperature in the pre-heater reaches the value at which it
has been set and causes the resistances to be disinserted (an opening of the contact of the regulation thermostat);
therefore, the fuel oil in the pre-heater should be at maximum temperature.
The control box (cyclic relay) of the burner is therefore connected by the regulation thermostat of the pre-heater
when it excludes the resistances by disinserting the relative relay.
Control box Safety Time
& relative in seconds
Programmer
LAL 1.25
Cyclic relay
The cyclic relay control box carries out the ignition programme by starting up the fan motor in order to effect the
pre-ventilation phase. If the air pressure supplied by the fan is sufficient to cause the intervention of the relative
pressure switch, the pump motor will be turned on immediately and will carry out a pre-circulation of hot oil in the
burner pipes. Oil from the pump reaches the pre-heated to the correct temperature and when it comes out it
passes through a filter before reaching the atomizer unit. The hot oil circulates in the atomizer unit without coming
out of the nozzle because the passages leading to the outward and return nozzles are closed.
This closure is carried out by "closing pins" applied to the ends of the rods.
These "pins" are pressed against their seats by strong springs which are situated at the opposite ends of the rods.
The oil circulates, comes out of the atomizer group return, goes through the sump where the TRU thermostat is
inserted and arrives at the return pressure regulator; it passes through this and reaches the pump return and from
there is discharged into the return. Hot oil circulation, as described above, is carried out at a pressure value
slightly higher (some bar) than the minimum pressure at which the return pressure regulator has been set
(10 ÷ 12 bar). The duration time of the pre-ventilation and oil pre-circulation phase is 22,5 seconds.
This time can be extended (theoretically indefinitely) because a special device in the electric circuit does not allow
the ignition programme to be carried out until the temperature of the fuel in the nozzle return pipeline has reached
the temperature at which the TRU thermostat (thermostat on the nozzle return) has been set.
This special device does not allow the fuel to pass through the nozzle until it has reached at least the temperature
at which the TRU thermostat has been set. Normally, intervention of the TRU thermostat takes place within the
pre-ventilation time 22,5 seconds); if it does not, pre-ventilation and fuel oil pre-circulation are extended until the
intervention of the TRU thermostat. The intervention of the TRU thermostat (oil in circulation sufficiently hot)
allows the control box to proceed with carrying out the ignition programme by inserting the ignition transformer
which in turn feeds the electrodes with high voltage. High voltage between the electrodes primes the electric
spark for ignition of the fuel/air mixture. 5 seconds after the ignition spark appears, the control box carries voltage
to the magnet, which by means of appropriate levers, moves backwards the two rods which intercept the flow
(outward and return) of fuel to the nozzle. This moving backwards of the rods also determines a closing of the
passage (by-pass) inside the atomizer unit. Consequently, the pump pressure is taken to the normal value of
about 20 ÷ 22 bar. Deviation of the two rods from the closing seat, now permits the fuel to enter the nozzle at the
pressure at which the pump has been regulated at (20 ÷ 22 bar), and comes out of the nozzle adequately atomized.
The return pressure, which determines delivery to the furnace, is regulated by the return pressure regulator.
The value of the ignition flow rate (minimum delivery) should be about 10 ÷ 12 bar).
The atomized fuel which comes out of the nozzle is mixed with air supplied by the fan and is then ignited by the
spark of the electrodes. Flame presence is detected by the photoresistant. The programme proceeds and, after 5
seconds, surpasses the "shut down" position, disconnects the ignition, and then connects the delivery regulating
circuit (fuel/air).
Control box specifications
Pre-Ventilation & Oil
Pre-circulation Time
in seconds
5 22,5
Pre-ignition Time Post-ignition
in seconds
2,5
37
Time between
Time 1st flame & Start
in seconds of Modulation
in seconds
20
5