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Considering the pressure in the combustion chamber
If the resistance value of the system "Combustion chamber - flue-
ways - stack" is constant, the combustion chamber pressure
changes in proportion to the gas and combustion air pressure as
the burner's output changes.
If, however, the combustion chamber pressure does not change
in proportion to the gas or air pressure, which is the case in plants
using a flue gas fan or a modulating flue gas damper, for in-
stance, a compensating circuit is required.
This circuit should also be used if pressure shocks or vibrations,
which adversely affect burner start-up, occur in the combustion
chamber during the start-up sequence.
It must always be taken into account that the burner output de-
creases as the combustion chamber pressure increases, and
vice versa.
6.9.2
Installation
All installation must be carried out by qualified per-
sonnel only.
WARNING
SKP75 is easily mounted on the square flange of any VG... valve
by means of 4 screws.
No gaskets or seals are required when mounting the actuator.
The square mounting flange can be rotated in steps of 90° pro-
viding four different mounting positions. The actuator can be
mounted or replaced while the gas valve is under pressure.
The actuator should be mounted so that the stroke position indi-
cator is clearly visible.
The pressure connection pipes should be as short
as possible to allow the regulator to react to sud-
den changes.
WARNING
The connection pipe for the combustion chamber
pressure must be installed so that condensing flue
gases cannot enter into the regulator but run back
into the combustion chamber. If necessary, a wa-
ter separator must be installed.
6.9.3
Start-up
1
Set the gas to air ratio to the desired value using adjusting
screw 1 on the left (rough setting) and then set the working
characteristic using adjusting screw 2)(Fig. 30) with the
small flame symbol, moving it towards zero.
2
Start the burner and run it at approximately 90% of full
capacity.
3
Measure CO
or O
content in the flue gases and correct
2
2
the ratio by adjusting screw 1 until optimum values are
obtained.
4
Return to low fire and measure the CO
flue gases.
If necessary, correct the setting by adjusting screw
2)(Fig. 30) until optimum values are obtained.
5
Limit the damper position for low fire operation (see servo-
motor adjustment).
The markings on the adjusting screws have the following mean-
ing:
+
more gas
-
less gas
If a significant parallel displacement of the working characteristic
was necessary to obtain optimum CO
mum output operation, the adjustment of the pressure ratio at
nominal load or at 90% of the nominal load must be checked
again and corrected if necessary.
20036762
Start-up, calibration and operation of the burner
or O
content in the
2
2
and O
values at mini-
2
2
6
Run the burner at the required output and limit the air
damper position or adjust intake to a partial setting.
If, with the servomotor fully opened, the air is insufficient to
guarantee the maximum required output, reset the combus-
tion head to the following numerically higher notch, thus
increasing head opening and therefore air delivery.
In any case air pressure (PA) at burner head must not
exceed the maximum value of 50 mbar.
7
Check the flue gas values at several intermediate output
levels. If corrections are necessary, note the following:
- adjust the pressure ratio screw 1)(Fig. 30) at high fire
operation only;
- adjust the bias screw 2)(Fig. 30) at low fire operation
only.
When firing at maximum burner capacity, ensure
that the SKP75... /VG... is not in the fully open po-
sition. If this is the case, either the gas valve is
WARNING
sized too small or the gas supply pressure is too
low.
4
5
S8332
Key (Fig. 30)
1
Adjustment and indication of the gas to air ratio
2
Adjustment and indication of working characteristic's parallel
displacement
3
Test point for the combustion chamber pressure
4
Test point for the gas pressure
5
Test point for the combustion air pressure
6
Stroke indication
30
GB
1
2
6
3
Fig. 30
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