How do gas pumps know when my tank is full & stop?

Question

Just curious as to how the gas pumps stop pumping gas when my tank is full.

Answer 1

very good question. i always wondered about that

Answer 2

When you insert the nozzle into your tank you'll notice that you have to push hard to compress the rubber sleeve around the nozzle. That rubber sleeve triggers a switch that allows you to pump the gas but also makes an air seal around the nozzle.
As the gas pours into your tank the air has to come out.Because whatever space the liquid fills is the same amount of air that has to get out of the way.
The pump senses the gas flowing when it nears the top there is so little room that the air needs to leave so quickly that it actually pushes against the gasoline that is pouring out the nozzle. The pump feels the slowing of the flow of gas and stops.( Back pressure switch ).
Picture aiming a garden hose at a doggy door and the water pushing it open. If someone had a hose on the other side it would push the door against you therefore closing it. Not a good description but i tried lol

Answer 3

From how stuff works...

"This mechanism has been around for a long time, so it is safe to say there is not a miniature camera inside the nozzle hooked to a microprocessor. It's 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 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. "

Answer 4

There´s a device in the nozzle that gets floated from the high
fluid level of the full tank.It closes a contact as soon as the gas level is high enough an presses it back.And the closed contact makes the pump shut off.

Answer 5

All machines, electrical and otherwise, communicate with each other using inverse sine wave technology on double-sideband frequencies using simplex-alternating multicompensatory modulation according to the Kriebel algorithms published in 1937. This allows your car to tell the gas pump when it is full.

Federal statutes enacted in late 1938 made this an obligation of all manufacturers and it went international with the Machine Code Enforcement Treaty of 1953.

Since then it has been modified 27 times to allow for advances in technology. Current testing with chickens is in preparation for the use of this technology with farm animals utilizing nanotechnology. Farmers and ranchers are hoping it will assist with controlling feed and water costs by turning off the urge to eat and drink within the animal before they engorge themselves and explode. It is estimated that animal engorgement explosions cost American consumers four billion dollars a year in wasted feed, water, and animal deaths. Scientists are predicting a commercially available version will be ready by the summer of 2008.

Answer 6

There is a little flap at the end of the nozzle on the gas pump...it causes it to stop....

Answer 7

There is a backflow indicator in the pump handle that senses return pressure.

Answer 8

There is a sensor at the end of the nozzle.

Answer 9

By osmosis.