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• 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”. Visually check the flame and adjust the combustion
air, if necessary, following the instruction in point 17. Then,
use the appropriate instruments to check combustion and, if
necessary, modify the previous setting checked only with a
visual inspection. The above-described operation must be
repeated by proceeding progressively (by advancing the disk
about 12° at a time) and each time modifying, if necessary, the
fuel-air ratio throughout the entire modulation stroke.
Make sure that the fuel output is progressive and gradual, and to
have the maximum output at the end of the modulation stroke.
This condition is necessary to ensure that modulation operation
is gradual enough. Change the fuel control screw positioning in
order to fulfil the above-mentioned condition. Note that maximum
flow is attained when return pressure is about 2 - 3 bar less
than delivery pressure (generally 20 - 22 bar). A correct air-fuel
ratio should give a carbon dioxide (CO
2
) value that increases
as fuel flow increases: as a rough 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
2
value of 13%
so as to prevent operation with a rather limited excess of air,
which could lead to a significant increase in smoke opacity due
to unavoidable causes (changes in atmospheric pressure, small
dust deposits in the fan air ducts etc.). Smoke opacity is strictly
connected to the type of fuel used (the most recent provisions
regarding this matter indicate no. 6 in the Bacharach scale as
maximum value). We recommend that you keep smoke opacity
at a value lower than 6 in the in the Bacharach scale even if the
CO
2
value could consequently be slightly lower. Reduced opacity
soils the boiler less and the average efficiency of the latter is
normally higher even if CO
2
levels are slightly lower. Remember
that a good adjustment requires the system temperature to be
at the standard operating degree, and the burner being working
since at least 15 minutes. If the appropriate instruments are not
available, evaluation can be based on the colour of the flame.
We recommend that the adjustment is performed so as to obtain
a soft light orange flame; avoid red flames with smoke and white
flames with an excess of air.
• 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”. With this setting the modulation function
will be enabled automatically only in response to requests
from the boiler probe. It is not normally necessary to act on the
internal adjusters of the power regulator; however, the relevant
instructions are to be found in the pamphlet..
Summary of Contents for GI MIST 1000 DSPGM
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