A good description of the workings of the automatic shutoff of a gas pump nozzle when the tank is full. In the comments weehoo4430 elaborates:
I’m an engineer and I used to work for the company that originally created that design. Actually, I redesigned that ball bearing mechanism. I can confirm that you are correct in your assessment of how it works. Also, most gas nozzles have a second diaphragm or plunger (not membrane) that deflects when there is pressure in the fuel line. It is used for prepay fill up. When you hit the prepay amount the dispenser shuts off, the pressure in the nozzle drops and that second diaphragm which is spring biased up will move and shut the nozzle off. There is a third shutoff in some nozzles that is called an attitude device. When a … moron… pulls a flowing nozzle out of a car’s fill pipe, a ball bearing blocks the pickup tube and shuts the nozzle off.
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