How does a gas pump detect when to stop flowing fuel into your tank?

Apr 15, 2008 by acmoore92 | Posted in Safety

A few weeks ago, I had the gas pump goin 'as fast as he could, held the handle all the way and supported by the little thing. I looked at the screen when it was about the limit of my tank, but never stopped pumping. Only gasoline keeps shooting, and overflowed into my hand and soil. How is the machine can detect when to stop pumping, and how it might have gone wrong in my case?

In a gas pump handle has two valves: the main valve, which is driven by the trigger to push large so that the gas flow, and the check valve, allowing gas flow outward, but it is nothing to change again, thus reducing fire risk. The valve seat has a small hole.

To the rear of this hole has been connected a Y-shaped tube

A branch of this tube runs out the tube and out through the tip while the other runs back to a diaphragm connected to a release mechanism of the main valve.

Pulling the trigger pump gas, operating beyond the hole in the valve draws air from the Y-shaped tube

(This is due to Bernoulli's principle: a stream of liquid in motion tends to throw things on the sides. Take my word for it.)

While the end of the Y-shaped tube of the nozzle exit is blocked, the air is simply drawn into the tube and not much else happens.

However, as soon as the gas in their car filling up tube is high enough to cover the pipe end, a partial vacuum is created in them, pulling on the diaphragm, the main valve communicated, and turn off the gas.

If gas becomes especially foam one day, can trigger the release mechanism early, with the result that you end up with less than a full tank of gas.