We may not realize this, but the fuel nozzles found in millions of filling stations around the world are actually beautiful mechanisms based on old-school mechanical principles. Here’s how they work.

Just look at that fuel nozzle cutaway in the video above— it’s a true thing of beauty! There are valves, diaphragms, linkages, springs, orifices, seals— it’s wonderful! And it all works to make sure your fuel winds up in your car’s tank, and not all over the pavement.

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Some of highlights include: a fuel-tank shutoff feature, attitude shut-off, and a no-pressure-no-flow device. The fuel-tank shutoff makes sure you don’t overfill your tank, and works in a similar way to a carburetor, in that the low pressure caused by a narrowing in a fluid flow path draws in another fluid.

In the case of a carburetor, a narrowing in the flow-path (this narrowing is called a venturi) of the incoming air draws in fuel, and in the case of a fuel nozzle like the one in the video, the venturi through which fuel flows actually draws in air from the sensing hole at the bottom of the spout.

The small hole on the side is the sensing port. Photo: Husky Corporation/YouTube (Screengrab)

As long as the sensing hole isn’t covered, air gets sucked into the venturi and mixes with the fuel that goes into your car. But if you cover that hole with your hand or with fuel (like when your tank fills up), the venturi will “struggle” to suck in the heavier fluid, and will therefore create a vacuum. This vacuum then sucks on a diaphragm, and shuts off the nozzle.

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Also on modern fuel nozzles is a no-pressure-no-flow feature ensuring that, once the pump is off (for example, when your money runs out of your pre-payed allotment), the lack of pressure from that pump closes a valve, shutting off the nozzle until the next user pulls the lever. This feature makes sure that someone can’t just leave the lever in the “open” position and cause the next customer to “take a bath” when the pump cuts back on.

Then there’s an attitude shutoff feature, also called an “Over-Horizontal Shut-Off mechanism,” which senses when the tip of the nozzle is higher than the inlet of the hose, moving a ball valve to cover the previously-mentioned vacuum tube (used for the fuel-tank shutoff feature), which then sucks on the diaphragm and closes the main valve.

Who knew there was so much cool stuff going on inside of those fuel-spewing nozzles that take all of our money.