WEBVTT - How does a gas pump know when the fuel tank is full?

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<v Speaker 1>Welcome to Brainstuff from the house stuff works dot com

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<v Speaker 1>where smart happens. Hi Am Marshall Brain with today's question.

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<v Speaker 1>How does a gas pump know when the fuel tank

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<v Speaker 1>is full so it can cut off automatically. This mechanism

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<v Speaker 1>has been around for decades, so it's safe to say

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<v Speaker 1>that there's not a miniature camera inside the nozzle looking

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<v Speaker 1>down into the tank and interpreting whether the tank is

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<v Speaker 1>full or not. This mechanism is purely mechanical and it's ingenious.

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<v Speaker 1>Near the tip of the nozzle there's a small hole

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<v Speaker 1>and a small pipe leads back from the hole into

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<v Speaker 1>the handle. Section is applied to this pipe using a venturi.

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<v Speaker 1>When the tank is not full, air is being drawn

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<v Speaker 1>through the hole by the vacuum, and the air flows easily.

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<v Speaker 1>When gasoline in the tank rises high enough to block

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<v Speaker 1>that that hole, a mechanical linkage in the handle senses

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<v Speaker 1>the change in section and flips the nozzle off. Here's

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<v Speaker 1>a way to think about it. You've got a small

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<v Speaker 1>pipe with section being applied at one end and air

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<v Speaker 1>flowing through the pipe easily. If you stick the free

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<v Speaker 1>end of that pipe into a glass of water, much

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<v Speaker 1>more section is needed, so a vacuum develops in the

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<v Speaker 1>middle of the pipe. That vacuum can be used to

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<v Speaker 1>flip a lever that cuts off the nozzle. The next

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<v Speaker 1>time you fill up your tank, look for this hole

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<v Speaker 1>in the small pipe, either on the inside or the

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<v Speaker 1>outside of the tip of the nozzle assembly. Do you

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<v Speaker 1>have any ideas or suggestions for this podcast? If so,

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<v Speaker 1>please send me an email at podcast at how stuff

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