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6.6
Adjustment before first firing (gas operation)
Adjustment of the combustion head has been illustrated on
page 26.
In addition, the following adjustments must also be made:
open manual valves up-line from the gas train.
Adjust the minimum gas pressure switch to the start of the
scale.
Adjust the maximum gas pressure switch to the start of the
scale.
Adjust the air pressure switch to the zero position of the
scale.
Purge the air from the gas line.
Continue to purge the air (we recommend using a plastic
tube routed outside the building) until gas is smelt.
Fit a U-type manometer or a differential pressure gauge
(Fig. 26), with the (+) fitting on the header gas pressure tap
and (-) fitting in the combustion chamber.
The manometer readings are used to calculate MAX. burner
power using the Tab. M at page 24.
Connect two lamps or testers to the two gas line solenoid
valves to check the exact moment at which voltage is sup-
plied.
This operation is unnecessary if each of the two solenoid
valves is equipped with a pilot light that signals voltage pass-
ing through.
6.7
Burner starting
Close the control devices and set switch 1)(Fig. 27) to "MAN" po-
sition.
Make sure that the lamps or testers connected to the solenoids,
or pilot lights on the solenoids themselves, indicate that no volt-
age is present.
If voltage is present, then immediately stop the burner and check
electrical connections.
6.8
Burner firing
Having completed the checks indicated in the previous heading,
the burner should fire. If the motor starts but the flame does not
appear and the control box goes into lock-out, reset and wait for
a new firing attempt.
If firing is still not achieved, it may be that gas is not reaching the
combustion head within the safety time period of 3 seconds.
6.9
Proportioning gas valve with air/gas ratio controller
6.9.1
Description
The SKP75 controls the gas pressure as a function of the com-
bustion air pressure so that the gas to air ratio remains constant
over the entireoutput range of the burner.
Using the SKP75, a separate gas pressure governor is not re-
quired. The gas train is this shorter, simpler and offers consider-
able savings.
Design features of the controller
The controller is fitted to the housing of the valve actuator and
has two diaphragms 1)(Fig. 28) which, via a lever system, act on
a ball valve 2) located in a bypass 3) of the pump 4).
20036762
Start-up, calibration and operation of the burner
Before starting up the burner it is good practice to adjust the gas
train so that ignition takes place in conditions of maximum safety,
i.e. with gas delivery at the minimum.
D3251
0 AUTO MAN
D3108
In this case increase gas firing delivery. The arrival of gas at the
sleeve is indicated by the U-type manometer (Fig. 26).
Once the burner has fired, now proceed with global calibration
operations.
The pressure of the combustion air acts on one diaphragm, the
gas pressure downstream of the valve on the other.
The gas to air pressure ratio can be adjusted from 0.4 to 9 and
the selected value is indicated in a viewing glass.
The selected characteristic for the pressure ratio can also be dis-
placed parallel (+/-), either towards "excess air" or "lack of air", to
increase the amount of air at low-fire levels, for example.
The extent of parallel displacement is indicated in another view-
ing glass. The controller can be adjusted during burner operation.
Depending on pressure conditions, the control accuracy is be-
tween 2 and 10%.
28
GB
1
2
-
+
Fig. 26
Fig. 27
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