Air Pressure Switch; Minimum Gas Pressure Switch - Riello 20194153 Installation, Use And Maintenance Instructions

5.6.4

Air pressure switch

Adjust the air pressure switch after performing all other burner
adjustments with the air pressure switch set to the start of the
scale (Fig. 34).
With the burner operating in the 1st stage, increase adjustment
pressure by slowly turning the relative knob clockwise until the
burner locks out.
Then turn the knob anti-clockwise by about 20% of the set point
and repeat burner starting to ensure it is correct.
If the burner locks out again, turn the knob anti-clockwise a little
bit more.
In conformity with the standard, the air pressure
switch must prevent the CO in the flue gases from
exceeding 1% (10,000 ppm).
To check this, insert a combustion analyser into
WARNING
the chimney, slowly close the fan suction inlet (for
example with cardboard) and check that the burn-
er locks out, before the CO in the fumes exceeds
1%.
The incorporated air pressure switch can work in a 'differential'
mode if connected with two pipes.
If a negative pressure in the combustion chamber during pre-
purging prevents the air pressure switch from switching.
Switching may be obtained by fitting a second pipe between the
air pressure switch and the suction inlet of the fan.
In such a manner the air pressure switch operates as differential
pressure switch.
The use of the air pressure switch with differential
operation is allowed only in industrial applications
and where rules enable the air pressure switch to
control only fan operation without any reference to
WARNING
CO limit.
D521
5.6.5

Minimum gas pressure switch

The purpose of the minimum gas pressure switch is to prevent
the burner from operating in an unsuitable way due to too low gas
pressure.
Adjust the minimum gas pressure switch (Fig. 35) after having
adjusted the burner, the gas valves and the gas train stabiliser.
With the burner operating at maximum output:
– install a pressure gauge downstream of the gas train stabilis-
er (for example at the gas pressure test point on the burner
combustion head);
20194185
Start-up, calibration and operation of the burner
Fig. 34
– choke slowly the manual gas cock until the pressure gauge
detects a decrease in the pressure read of about 0.1 kPa
(1 mbar). In this phase, verify the CO value which must al-
ways be less than 100 mg/kWh (93 ppm).
– Increase the adjustment of the gas pressure switch until it in-
tervenes, causing the burner shutdown;
– remove the pressure gauge and close the cock of the gas
pressure test point used for the measurement; open com-
pletely the manual gas cock.
1 kPa = 10 mbar
WARNING
28 GB
D3855
Fig. 35