| Above the surface of the fuel in the tank, more or less fuel vapours are created, depending on air pressure and ambient temperature. |
| The activated charcoal filter system prevents these HC emissions from escaping into the air we breath. |
| The fuel vapours, in reduced quantities, arrive at the activated charcoal filter from the highest point in the fuel tank via the gravity safety valve (it closes at an angle of 45°) and via the breather valve. |
| The activated charcoal absorbs these vapours like a sponge. |
| Running, with lambda control activated (engine warm), the control unit, according to engine load and revs, excites the fuel tank breather valve -N80-, also called the regeneration valve, at impulses. The opening timing depends on the signals received. |
| During the scavenging process (regeneration of the activated charcoal), outside air passing through the ventilation chamber in the upper part of the activated charcoal filter is drawn in by the vacuum at the intake manifold. The temporarily accumulated fuel vapours and the outside air in the activated charcoal are added in doses for combustion. |
| The breather valve prevents the combustion vapours being drawn into the fuel tank when the tank breather valve is open and there is a vacuum at the adjacent intake manifold. In this way, emptying of the activated charcoal filter is ensured beforehand. |
| Without voltage (e.g. an open circuit in the wiring) the fuel tank breather valve closes. The activated charcoal filter is not emptied. |
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