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Speaker 1: Welcome to brain Stuff from how stuff works dot com,

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Speaker 1: where smart happens High Marshall Brain. Next time you're filling

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Speaker 1: up your tank at a gas station, ask yourself this,

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Speaker 1: How does the nozzle know when the tank is full? No,

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Speaker 1: there's not a miniature camera inside the nozzle hooked to

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Speaker 1: a microprocessor. This mechanism has been around for decades. It's

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Speaker 1: purely mechanical and ingenious. Near the tip of the nozzle

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Speaker 1: is a small hole and a small pipe leads back

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Speaker 1: from the hole into the handle. Suction is applied to

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Speaker 1: this pipe using a ventur e. When the tank is

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Speaker 1: not full, air is being drawn through the hole by

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Speaker 1: the vacuum, and the air flows easily. When gasoline in

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Speaker 1: the tank rises high enough to block the hole, a

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Speaker 1: mechanical linkage in the handle senses the change in section

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Speaker 1: and flips the nozzle off. Here's a way to think

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Speaker 1: about it. You've got a small pipe with suction being

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Speaker 1: applied at one end and air flowing through the pipe easily.

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Speaker 1: If you dick the free end of the pipe and

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Speaker 1: a glass of water, much more section is needed, so

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Speaker 1: a vacuum develops in the middle of the pipe. That

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Speaker 1: vacuum can be used to flip a lever that cuts

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Speaker 1: off the nozzle. The next time you fill up your tank,

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Speaker 1: look for this hole, either on the inside or the

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Speaker 1: outside of the tip of the handle. Do you have

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Speaker 1: any ideas or suggestions for this podcast? If so, please

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Speaker 1: send me an email at podcast at how stuff works

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Speaker 1: dot com. For more on this and thousands of other topics,

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Speaker 1: go to how stuff works dot com.