The gas pump is made up of two components. There's the mechanical component, which actually does the work of pumping the gas into your car. Then there's the computer, which tells the mechanical component what to do and monitors how much gas you've pumped so that it knows what to charge.

The fuel at the gas station is kept in underground tanks and is pumped up to the surface and into your car by a pump motor. When you select the grade of gas you want before you start pumping, the computer tells the blend valve to go to work. The blend valve is responsible for mixing the various types of fuel stored in the fuel tanks to provide the correct blend of gas.

As the right blend of gas is pumped from the underground tanks to your car, it passes through a flow control valve which regulates the speed of the gasoline flow. Information about the fuel passing through the flow control valve is passed on to the computer, which in turn displays the litres (and dollars) you're putting in to your car.

As you know, when your tank is full, the nozzle handle releases, shutting off the flow of gas. This is because there's a small hole near the tip of the nozzle and a small pipe inside that leads back to a shutoff mechanism. This tube constantly sucks in air while you're filling the tank. As the gas level in your tank rises, the air continues to flow - but when the gas reaches the level of the pipe, the air pressure inside the tube drops. The shutoff mechanism in the pump handle senses the change in suction and trips the nozzle off. So…very similar to elves.

Thus ends our overview of how the gas pump function - if you're looking for a more in-depth look at how the gas pump works, be sure to check out How Stuff Works .

- Rose R.