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 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 the hole, a mechanical linkage in the handle senses the
change in suction 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 stick the
free end of the pipe in a glass of water, much more suction 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 either on the inside
or the outside of the tip.
from
http://www.howstuffworks.com/
Richard
"rads" <
[email protected]> wrote in message
news:
[email protected]...
> Suspect I should know this, but it's bothering me and I don't seem to
> be able to do any proper work today until I find out "How does a
> petrol pump nozzle know when your tank is full and switch itself off?"
>
> I have googled without result so over to the collective wisdom of
> a.f.l to put me out of my misery.
>
> TIA
>
> David
