| Depending upon the air pressure and ambient temperature, fuel vapour will form above the level of fuel in the tank. |
| The activated charcoal filter system prevents these HC emissions escaping to the atmosphere. |
| In limited quantities, fuel vapours pass through a gravity valve (which closes at an angle of 45°) located at the highest point in the tank and through a pressure retention valve into the activated charcoal filter. |
| The activated charcoal stores these vapours like a sponge. |
| When the car is being driven and the lambda control is active (engine warm), the activated charcoal filter solenoid valve 1 -N80-, also known as regeneration valve, is activated (pulsed) by the engine control unit depending upon load and engine speed. The opening period depends on the input signals. |
| During the purging procedure (regeneration of the activated charcoal), the intake manifold vacuum draws in fresh air through the vent opening on the underside of the activated charcoal filter. The fuel vapours stored in the activated charcoal and fresh air are fed to combustion in metered quantities. |
| The pressure retention valve prevents fuel vapours from being drawn from the tank when the active charcoal filter system solenoid valve 1 -N80- is open and intake manifold vacuum is present. It thus ensures that the purging of the activated charcoal filter has priority. |
| When it is no energised (e.g. open circuit), the active charcoal filter system solenoid valve 1 -N80- is closed. The activated charcoal filter will not be purged. |
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| Hose connections are secured with either spring-type or clamp-type clips. |
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| Always replace clamp-type clips with spring-type clips. |
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| Spring-type clip pliers -VAS 5024- or hose clip pliers -V.A.G 1921- are recommended for installation of spring-type clips. |
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