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cally connected in series; thus,
the start (intended as circuit
opening) of any one of the gas
pressure switches does not
allow starting the control box
and thus, the burner. When
the burner is operating (flame
on), the start of the gas pres-
sure switches (circuit opening)
causes the immediate shut
down of the burner. Upon the
general test and inspection of
the burner, it is necessary to
check the correct operation of
the pressure switches. By suit-
ably acting on the respective
regulation members, make sure
that the pressure switch starts
(circuit opening), thus shutting
down the burner.
22) Only for BGN 540 Lx
In case of UV photoelectric
cell, after at least one minute
from ignition extract the pho-
toelectric cell from its housing.
When the UV photoelectric cell
is extracted from its housing,
it cannot "see" the ultraviolet
radiation emitted by the flame
and thus, the relevant relay
de-energises. The burner im-
mediately shuts down in "lock".
A light greasiness strongly affects
the passage of ultraviolet beams
through the UV photoelectric
cell bulb, thus preventing the
internal photosensitive element
from receiving the necessary
radiation for a correct operation.
If the bulb is dirty with light oil,
heavy oil, etc., clean it accu-
rately. Note that a simple finger
contact can cause a light greasi-
ness, sufficient to impair the UV
photoelectric cell operation. The
UV photoelectric cell does not
"see" daylight or the light of a
common candle. A possible sen-
sibility check can be made with
a flame (lighter, candle) or with
the electrical discharge occur-
ring between the electrodes of
a common ignition transformer.
To ensure a correct operation,
the UV photoelectric cell current
value must be sufficiently stable,
and must not decrease below
the minimum value required for
All manuals and user guides at all-guides.com
the specific control box. Said
value is shown in the wiring
diagram. It may be necessary
to experimentally search the
best position by making the
body containing the photoelec-
tric cell slide (axial or rotation
movement) with respect to the
fixing clamp.
23) Check the efficiency of the
boiler thermostats or pressure
switches (their start must shut
down the burner).
AIR REGULATION ON
COMBUSTION HEAD
(See dr. n° 0002933310)
Warning:
When, as in this case, the burner
is provided with gas valves model
MB-VEF.., DMV-VEF.., by moving
the air regulation device on the
combustion head there automati-
cally and unavoidably occurs a
gas output variation (see chapter
Valve operation principle, model
MB-VEF.., DMV-VEF..).
The combustion head is equipped
with a regulation device, so as to
open or close the air passage be-
tween disk and head. By closing
the passage, it is thus possible to
obtain a high pressure upstream of
the disk also for low flow rates. The
high air speed and turbulence allows
a better penetration of the same into
the fuel and therefore, an excellent
mixture and flame stability. It may be
necessary to have a high air pres-
sure upstream of the disk, so as to
prevent flame pulses. This condition
is indispensable when the burner
operates on pressurised combustion
chamber and/or with high heating
load. From what said above it is
evident that the device closing the
air on the combustion head must be
set to such position as to always
obtain, behind the disk, a very high
air pressure value. It is advisable
to regulate so as to have such air
closure on the head as to require the
opening of the air damper regulat-
ing the flow of the burner ventilator
suction. Of course, this condition
must only occur when the burner is
49 / 119
0006081062_200709
operating at the maximum desired
output. In practice, the regulation
must start with the device that closes
the air on the combustion head in an
intermediate position, igniting the
burner for an indicative regulation
as explained above.
When the maximum desired out-
put is reached, correct the position
of the device closing the air on
the combustion head by moving
it forwards or backwards so as to
have a suitable air flow for the out-
put, with suction air regulation
damper sensibly open (see dr. n°
0002933310).
N.B. To facilitate the combustion
head regulation, see table (dr. n°
0002933200)
When reducing the air passage
on the combustion head, avoid
closing it completely, which may
cause an excessive heating of
the head with a consequent quick
deterioration. Perfectly adjust to
central position with respect to
the disk. Note that if not perfectly
centred with respect to the disk
may cause a wrong combustion
and an excessive head heating,
with a consequent quick dete-
rioration. The check is carried out
by looking through the inspection
hole on the rear side of the burner.
Afterwards, tighten the screws lock-
ing the position of the air regulation
device on the combustion head.
N.B.:
Check that ignition is regular be-
cause if the controller has been
moved forward, the output air speed
could be so high as to make igni-
tion difficult. In such a case, it is
necessary to move backwards,
degree by degree, the regulator
until reaching the position in which
the ignition is regular and accept
this new position as definitive.
We still remind you that it is prefer-
able, for the small flame, to limit
the air quantity to the minimum in-
dispensable to have a safe ignition
even in the most demanding case.
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