How does a gas station nozzle know to stop?

[jsinger]

Got into a big argument yesterday over how automatic
pumps at gas stations turn off the gas flow just before a tank is full and before gasoline touches the tip of the nozzle. How does that miracle happen?

When my time comes, this will be the second question
I ask God. First question: what does he have against the Chicago Cubs

[mattglet]

God gave the Lovable Losers their one chance last year. Bartman took it away. Sorry!

;)

[Quinn]

Vacuum [auto.howstuffworks.com]

[yokelrobin]

There's a little man in a boat in your gas tank. As the tank fills up, he rises.

There's another little man in the end of the nozzle. When he hears a "Melp!" he stops the gas flowing.

Listen carefully next time.

[Macguru]

>>There's a little man in a boat in your gas tank.

:)

See what happens [katu.com] when the little man is a smoker.

[TheDoctor]

Nasty. I remember something like this happening at an oil terminal when I worked in the oil industry, and an official investigation not being able to work out what happened. Sadly, the driver died in that incident.

But I notice that neither the man in question nor the journalist who wrote up the story knows much about motor spirit:

Walker credits the fact that gas fumes rather than the liquid itself caught fire at first, letting him scramble away unharmed.

The liquid is not flammable. It has to evaporate before it will burn, which is why an almost empty tank is more dangereous than a full one.

[Macguru]

Of course, all fuels needs an oxydant to explode...

<steering even more off topic> It about time occident needs less fuel, else...

Lucky nozzles know when to stop, cause humans dont.

[jsinger]

Back to the vital subject at hand (better yet, some distance away):

I'm still not crystal clear on how the vacuum thingie works. Apparently the gasoline liquid has to rise above the nozzle's tip thereby closing off that small hole. Is that right?

[SEOMike]

Ever hear all the bubbling just after the pump clicks off? I'll bet it's those bubbles that rise to the top of the fuel filler tube that cause the vacuum to change thereby shutting off the gas. That'd probably give at least 6 or so inches of fuel level (in the tube) before gas actually hit the tip.

Just a guess here... let me know if I'm wrong. :)

[webnerd]

There is a "build in computer chip" that is all knowing that automatically shuts the pump off
a) when your tank full
b) or due to the high price of gasoline when your credit limit has been reached
c) or when it detects that your are smoking (not installed on all pumps yet obviously).

[lgn1]

Who can afford to fill up the tank anymore. I just thrown $20 bucks in and ignore the fact that im visiting the service station more often these days.

Remember, apathy and denial are great stress relieving tools :)

[jsinger]

More than you'd ever want to know about gas nozzles:

[wonderquest.com...]

[edited by: lawman at 8:07 pm (utc) on July 7, 2005]