Speaker 1: Welcome to Brainstuff from the house stuff works dot com
Speaker 1: where smart happens. Hi Am Marshall Brain with today's question.
Speaker 1: How does a gas pump know when the fuel tank
Speaker 1: is full so it can cut off automatically. This mechanism
Speaker 1: has been around for decades, so it's safe to say
Speaker 1: that there's not a miniature camera inside the nozzle looking
Speaker 1: down into the tank and interpreting whether the tank is
Speaker 1: full or not. This mechanism is purely mechanical and it's ingenious.
Speaker 1: Near the tip of the nozzle there's a small hole
Speaker 1: and a small pipe leads back from the hole into
Speaker 1: the handle. Section is applied to this pipe using a venturi.
Speaker 1: When the tank is not full, air is being drawn
Speaker 1: through the hole by the vacuum, and the air flows easily.
Speaker 1: When gasoline in the tank rises high enough to block
Speaker 1: that that hole, a mechanical linkage in the handle senses
Speaker 1: the change in section and flips the nozzle off. Here's
Speaker 1: a way to think about it. You've got a small
Speaker 1: pipe with section being applied at one end and air
Speaker 1: flowing through the pipe easily. If you stick the free
Speaker 1: end of that pipe into a glass of water, much
Speaker 1: more section is needed, so a vacuum develops in the
Speaker 1: middle of the pipe. That vacuum can be used to
Speaker 1: flip a lever that cuts off the nozzle. The next
Speaker 1: time you fill up your tank, look for this hole
Speaker 1: in the small pipe, either on the inside or the
Speaker 1: outside of the tip of the nozzle assembly. Do you
Speaker 1: have any ideas or suggestions for this podcast? If so,
Speaker 1: please send me an email at podcast at how stuff
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