| Activated charcoal filter system-Operation |
| 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. |
| 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 active carbon filter in limited quantities. |
| The active carbon absorbs these vapours like a sponge |
| When the car is being driven and the lambda control is active (engine warm), the active carbon 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 is dependent on the input signals |
| Intake manifold vacuum draws fresh air through the vent opening on the underside of the activated carbon filter during the purging procedure (regenerating the activated carbon). The fuel vapours stored in the activated carbon 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 solenoid valve is open and intake manifold vacuum is present. It therefore ensures that the evacuation of the active carbon filter has priority. |
| When not energised (e.g. open circuit), the solenoid valve is closed. The active carbon filter will not be purged. |
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