17) When the burner is working at "minimum" adjust the air to
the quantity needed to ensure good combustion. Turn the
adjuster screws in or out at the point of contact with the lever
that transmits combustion air regulation damper movement.
The quantity of air at "minimum" should be a little scarce so
as to ensure perfect ignition even under the most demanding
circumstances.
18) After adjusting the air for the "minimum" turn the modulation
switches to position "MAN" and to position "MAX".
19) The modulation motor starts moving: wait for the disk (on
which the adjuster screws are fitted) to sweep through an
angle of about 12° (this corresponds to the space taken up by
three screws) and then stop modulation by turning the switch
back to position "0". Run a visual check on the flame and, if
necessary, regulate combustion air as described in point 17.
Then check combustion using the appropriate instruments
and, if necessary, correct the adjustment previously made by
E
way of visual check. The above-described operation must be
repeated by proceeding progressively (by advancing the disk
N
about 12° at a time) and, each time, modifying, where neces-
sary, the fuel-air ratio throughout the entire modulation range.
G
It is necessary to make sure that fuel feed progression occurs
gradually and that maximum fuel flow occurs at the end of the
L
modulation range. This condition is necessary for attainment
of smooth, gradual modulation. If necessary modify the posi-
I
tion of the fuel control screws to obtain that specified above.
Note that maximum flow is attained when return pressure is
S
about 2 - 3 bar less than delivery pressure (generally 20 - 22
bar). A correct air-fuel ratio should give a carbon dioxide
H
(CO
) value that increases as fuel flow increases: as a rough
2
guide, it should be at least 10% at minimum flow and reach
an optimum of about 13 % at maximum flow.
It is inadvisable to exceed a CO
operation with a rather limited excess of air, possibly leading to
a significant increase in smoke number owing to unavoidable
causes (changes in atmospheric pressure, small dust depos-
its in the fan air ducts etc.). The resulting smoke (i.e. fume)
number is closely linked to the type of fuel used (latest regula-
tions indicate n° 6 on the Bacharach scale as a maximum).
it is advisable, if possible, to keep the smoke number below
n° 6 on the Bacharach scale even if the CO
consequence, be slightly lower. Reduced opacity (i.e. a lower
smoke number) soils the boiler less and the average efficiency
of the latter is normally higher even if CO
lower. Remember that to achieve proper adjustment system
water must be up to normal working temperature and that the
burner must have been working for at least fifteen minutes. In
the absence of proper instrumentation use fume colour as a
guide. We recommend that adjustment be effected so as to
obtain a light orange flame; avoid red flames with smoke and
white flames with an exaggerated excess of air.
20) Now check that modulation works properly in automatic mode.
Turn the AUT - O - MAN switch to "AUT" and the MIN - O - MAX
switch to "O". The modulation system is now on and under the
exclusive automatic control of the boiler probe. It is not normally
necessary to act on the internal adjusters of the "RWF 40" power
regulator; however, the relevant instructions are contained in
the pamphlet.
figure of 13% so as to prevent
2
value could, as a
2
levels are slightly
2
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