Advertisement
DESCRIPTION OF OPERATION WITH FUEL OIL (see BT 8713/1)
During the fuel oil pre-heating phase, current passes through the pre-heater regulating thermostat and reaches
the remote switch coil of the heating elements. The remote switch closes and provides current to the pre-heater
heating elements which heat the fuel contained in it. The minimum temperature thermostat on the pre-heater
closes when the temperature reaches the set value. The equipment is only activated when the temperature at
which the heating elements switch off is reached (the contacts on the regulation thermostat open), therefore, with
the fuel oil in the pre-heater, at maximum temperature. The burner command and control unit (cycle relay) is then
activated by the pre-heater regulation thermostat when the heating elements are cut-out, disconnecting the rela-
tive remote switch.
Control box
Safety
and relative
delay
programmer
in seconds
LFL 1.333
3
Cycle relay
The cycle relay carries out the ignition program by starting the fan motor for the pre-ventilation phase.
If the pressure of the air supplied by the fan is enough to activate the relative pressure switch, the pump motor is also
immediately turned on and precirculates the hot oil through the burner's pipes.
The oil goes from the pump to the pre-heater, passing through it and becoming heated, and exiting through a filter before
going to the atomiser unit. The hot oil circulates in the atomiser unit without exiting through the nozzle, because the openings
to the nozzle (delivery) and from the nozzle (return) are closed. These are plugged by "closing pins" applied to the ends of
the shafts. These pins are pushed against the seats by strong springs, located at the opposite end of the shafts. The oil
circulates and exits through the return of the atomiser unit, passes through the trap with the TRU thermostat, reaches and
passes through the pressure regulator of the 1
reaches the pump return. From here it is discharged into the return. Circulation of the hot oil described above occurs at a
pressure slightly higher (a few bars) than the minimum pressure set on the return pressure regulator for the 1st flame
(10 - 12 bar). This ventilation and oil pre-circulation phase has a fixed duration. This time can be extended (theoretically to
infinity) since a control on the electrical circuit for the equipment prevents the ignition program from running until the
temperature of the fuel in the nozzle return piping has reached the temperature set on the TRU (Nozzle Return Thermostat)
thermostat. This means that the fuel cannot pass through the nozzle until its temperature is at least equal to that set on the
TRU thermostat. Normally, the TRU thermostat intervenes within the normal pre-ventilation time, otherwise, pre-ventilation
and pre-circulation of the oil is prolonged until the TRU thermostat cuts in. Intervention of the TRU (circulating oil sufficiently
hot) allows the equipment to proceed with the ignition program and activates the ignition transformer which feeds high
voltage to the electrodes. The high voltage between the electrodes triggers the electrical discharge (spark) which ignites the
fuel/air mixture. Once the ignition spark has been activated, the equipment powers the magnet which, by means of special
lever mechanisms, retracts the two shafts that cut off the flow (feed and return) of fuel to the nozzle.
Retraction of the shafts also closes the by-pass inside the atomiser unit, hence the pressure in the pump rises to a value
that is normally around 20 - 22 bar. Retraction of the two shafts from the closing seats allows the fuel to enter the nozzle at
the pressure set on the pump (20 - 22 bar), and to leave the nozzle adequately atomised. The return pressure, which
determines delivery to the combustion chamber, is now controlled by the return pressure regulator of the 1
st
For the 1
flame (minimum delivery), this value is around 10 - 12 bar. The atomised fuel leaving the nozzle mixes with the air
supplied by the fan and is ignited by a spark from the electrodes. Flame presence is detected by a UV photocell. The
programmer proceeds and passes beyond the cut-out position, disconnects the ignition, and then activates the 2
This operation occurs by feeding, through the relative thermostat of pressure switch, the air regulation servomotor that
controls the opening of air at the 2
special cam) of a contact that delivers power to the solenoid valve coil of the 2
fuel through the return pressure regulator of the 1
The flow of return fuel is now forced to pass through the pressure regulator of the 2
the value set on the regulator, hence the feed to the nozzle is increased and the burner works at maximum output. The
nozzle return pressure is about 18 - 20 bar, when the pressure at the pump is at 20 - 22 bar.
The delivery of fuel and air remains at maximum value until the temperature (or pressure if steam boiler) in the boiler
reaches the temperature set on the thermostat (pressure switch if steam boilers) of the 2
returning operation to the 1
alone is normally insufficient to maintain the pressure or temperature at the required level, which will continue to drop until
reaching the value at which the control device of the 2
delivery. The burner is completely stopped when, even with only the 1
cut-in value set on the control device (pressure switch or thermostat). The unit reignites automatically when the temperature
or pressure drops below the value set on the pressure switch or thermostat. It should be remembered that with good
combustion, delivery can be modified to around 1 to 1/3 the maximum flow rate shown on the label.
Control box Specifications
Preventilation /
air lock open time
in seconds
31,5
st
flame, through the solenoid valve (normally open) of the 2
nd
flame. Rotation of the air regulation servomotor causes the closing (by means of a
st
flame.
st
flame. Return to the 1
st
flame position results in a reduction in fuel and air delivery. The 1
Preignition
Postignition
in seconds
in seconds
6
nd
flame. This closes and shuts off the flow of
nd
flame (pressure switch or thermostat) reinstates total fuel and air
st
flame lit, the pressure or temperature reaches the
13
Time between 1st flame
& 2nd flame
in seconds
3
12
st
nd
flame, and the return pressure rises to
nd
flame, causing it to cut in,
nd
flame and
flame.
nd
flame.
st
flame
Advertisement
