Tank vent valve: Notes

The tank-ventilation system captures evaporated components of the fuel and feeds these to the combustion. The tank-ventilation system prevents hydrocarbons from escaping into the environment. On one hand, the fuel expands. If the pressure and temperature remain the same, however, evaporation decreases over time, as only the light hydrocarbons evaporate. On the other hand, if there were no tank-ventilation system, a partial vacuum would be created in the tank when fuel is withdrawn. This is why there is ventilation at the back of the tank.