How does the filling faucet?

You're probably wondering how the filling valve realizes that it is time to stop the flow of fuel when the tank is filled. No, it is not imposed elven spell, and built-in video cameras, sensors, and nanotechnology radiopoplavki here, too innocent. If you look down the barrel of a gun, then a major, large channel you will see a small canal.

This so-called vacuum channel, it leads to a ball valve in the top of the gun. Entering the gun displaces fuel from it, and without a small amount of air, and compensates for the pressure drop the gun, sucking through this small channel the air that there is in the fuel tank of a vehicle. Gradually replacing petrol tank of the air, the air ceases to flow into the vacuum port, ball valve "suffocating" and slams than triggers a blockage and the main valve (in this moment you hear a click).
VIA





Source: