Ever Wonder How a Gas Pump Knows When to Click Off? 'It's Actually Surprisingly Complicated

You're standing at the pump, watching the gallons and dollars tick higher and higher. Then, click, the pump stops. You're done.

But have you ever wondered how the nozzle knows your tank is full?

How does your gas pump know when to click off, signaling the tank is full? (Photo: Shutterstock.com)

The YouTube channel BrainStuff tackled this question.

"It's actually surprisingly complicated," host Josh Clark said.

It all involves the Venturi effect.

Picture a tube with a substance -- gas or liquid -- flowing through it. The center of the tube is pinched, causing the fluid coming out on the other side of the pinch to be compressed and changing pressure.

As the tank is filling, air goes freely up the tube keeping the diaphragm filled with air at the top of the nozzle. (Image via YouTube video screenshot)

On a gas nozzle, a hole at the end allows air to flow up a tube into an air sack in the handle. But when the tank becomes full and liquid covers the hole, sucking up denser gas into the tube instead of air, a change in pressure occurs. This collapses the air-filled sack, triggering the shutoff.

After the tank becomes full, gas fills the tube, changing the pressure and triggering the shutoff. (Image via YouTube video screenshot)

"Seriously, that's what's going on in your gas nozzle when you're pumping gas and it fills up," Clark said.

Watch Clark's explanation of how the Venturi effect triggers the gas nozzle to shut off:

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