If you have ever wondered how all those fuel nozzles at your gas station actually work…

…then you have come to the right place.

It’s a simple, yet complex, arrangement of mechanical components—linkages, valves, springs, diaphragms, seals—that work together to make these fascinating contraptions function.

Please explain…

How Gas Station Nozzles Work?

Let’s have a quick review of couple of concepts that we established in our physics classes, the understanding of which would be required to fully grasp the mechanics behind the functioning of a gas station nozzle.

• We know that a fluid flows from a high-pressure area to a low-pressure area.
• We know that the pressure in vacuum is less than the atmospheric pressure.

Now that we have reviewed the essential concepts, we can press the lever on the fuel nozzle to see how the whole thing works.

As you press the lever, it opens the main poppet valve

This poppet valve allows the gasoline to flow through the body of the fuel nozzle. However, this flow only lasts for a short term. To continue to draw more gasoline through the nozzle, the contraption has to pull-in additional force to assist the gasoline flow.  That is where the design of the device helps itself.

The initial flow of gasoline causes an anti-drain valve to move downwards

The downward movement of the valve, creates a low-pressure area within the fuel nozzle. This low-pressure area is connected to the spout of the gas pump nozzle via a tube—the point of insertion being a small hole present at the bottom of spout. This hole is exposed to the external environment, allowing air to enter.

When the vacuum is created, the resulting pressure drop causes air to flow from the small hole, all the way through the tube and into the vacuum space. There it mixes with gasoline, and the flow of air causes gasoline to maintain its own flow.

This flow continues until the gasoline level in the fuel tank reaches a certain point

At this point, the filled gasoline covers the small hole through which the air has been entering. When the hole is covered, instead of air, gasoline starts flowing through it and all the way up to the vacuum space.

Since gasoline is denser than air, the pressure changes in the vacuum space. This pressure change causes a diaphragm to be sucked, which then shuts off the main poppet valve. Consequently, the gasoline supply from the mains is cut off.

And this is how the fuel nozzles at your gas station works.

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