How gas pumps work

Next time you're filling up your tank at a gas station, ask yourself this: how does the nozzle know when the tank is full? Learn more about gas pumps in this HowStuffWorks podcast.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how stuff works dot com,
where smart happens High Marshall Brain. Next time you're filling
up your tank at a gas station, ask yourself this,
How does the nozzle know when the tank is full? No,
there's not a miniature camera inside the nozzle hooked to
a microprocessor. This mechanism has been around for decades. It's

(00:22):
purely mechanical and ingenious. Near the tip of the nozzle
is a small hole and a small pipe leads back
from the hole into the handle. Suction is applied to
this pipe using a ventur e. When the tank is
not full, air is being drawn through the hole by
the vacuum, and the air flows easily. When gasoline in

(00:43):
the tank rises high enough to block the 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 suction being
applied at one end and air flowing through the pipe easily.
If you dick the free end of the pipe and
a glass of water, much more section is needed, so

(01:04):
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, either on the inside or the
outside of the tip of the handle. Do you have
any ideas or suggestions for this podcast? If so, please
send me an email at podcast at how stuff works

(01:26):
dot com. For more on this and thousands of other topics,
go to how stuff works dot com.