How petrol filling nozzel work?
Answers:
As fuel comes out air goes in. When the tip of the nozzle is submerged or even splashed with liquid it briefly stops the airflow and a diaphragm releases the valve and stops the flow of fuel.
If you have a look up the nozzle you will see a small tube. this feeds back to the trigger and by a physical phenomena called venturi action the petrol passing into the car past the trigger pulls air up through the tube. At the top of the tube is a mechanism to distinguish between air and liquid (I assume a float, or spring action lever; i stand corrected by da maestro, it is a diaphragm. so its a change in air pressure in the tube that releases the trigger!).
When the tank is full the liquid covers the tube and liquid is sucked up through the tube. It hits the mechanism and releases the trigger. Dead simple, no power required and safe! (Flammable liquids and all that!)
I only read this question to find out the answer, Very interesting
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