MARMON ANGELO PO COMBISTAR FX, Техническое руководство, Страница: 62 / 178

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4. GAS SYSTEM - OPERATE TEST ADJUST INSTALL REPORT
4.1. System operation
4.1.1. Premixed system general principles
FX oven gas system is a "total premix", this means that the gas is completely mixed with
the necessary air to have "good" combustion and then the air-gas mixture is ignited at the
burner.
Therefore, the relationship between the quantity of air and the amount of mixed gas is
constant and must be properly adjusted to avoid being too rich (risk of production of CO)
or too poor (unstable flames).
In the diagram below we highlight the major differences between the blown system (FM)
and premixed system (FX): In the blown system, the gas and air inlet circuit to the burner
are separated, while in the premixed system both flow into the mixer before going into the
burner.
Consequently, in the blown system to adjust the gas flow and the combustion quality it is
enough to adjust the gas valve output pressure or replace the nozzle.
In the premixed system, however, the gas valve output pressure is zero because of the
vacuum created by the fan and therefore, only at low speeds (when the influence of the
blower decreases), the combustion is controlled by the gas valve offset. To make this
adjustment it is necessary to use a gas flue analyzer.
Furthermore, an electronic variable-speed blower, controlled by the power board, allows
you to change the quantity of the air-gas mixture.