How does a petrol pump (Service station pump) know when to stop? how does it know when the car is full?

Answer 1

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 2

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Answer 3

The pump knows when the tank is full when the level of fuel reaches the pump nozzle. At the and of the nozzle (look next time you put gas in) is a small hole and when the fuel reaches that hole it is closed off and a signal goes to the pump to stop filling. As for knowing how much is put in then it switches off, is done electronically. You put in a preset amount and the pump computer knows that that is x gallons is equal to x dollars, so when the volume is nearly reached the pump slows done and then stops at the preset amount!

Answer 4

Returning air pressure up the filler tube.

Answer 5

and how does a thermous know to keep hot things hot and cold things cold? how do it know