Welcome to Brainstuff from the house stuff works dot com where smart happens. Hi Am Marshall Brain with today's question. How does a gas pump know when the fuel tank is full so it can cut off automatically. This mechanism has been around for decades, so it's safe to say that there's not a miniature camera inside the nozzle looking down into the tank and interpreting whether the tank is full or not. This mechanism is purely mechanical and it's ingenious.
Near the tip of the nozzle there's a small hole and a small pipe leads back from the hole into the handle. Section is applied to this pipe using a venturi. When the tank is not full, air is being drawn through the hole by the vacuum, and the air flows easily. When gasoline in the tank rises high enough to block that that hole, a mechanical linkage in the handle senses the change in section and flips the nozzle off. Here's
a way to think about it. You've got a small pipe with section being applied at one end and air flowing through the pipe easily. If you stick the free end of that pipe into a glass of water, much more section is needed, so a vacuum develops in the middle of the pipe. That vacuum can be used to flip a lever that cuts off the nozzle. The next time you fill up your tank, look for this hole in the small pipe, either on the inside or the outside of the tip of the nozzle assembly. Do you
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