# ELI5 How does something become “pressurized” like in an airplane? What are some other examples?

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ELI5 How does something become “pressurized” like in an airplane? What are some other examples?

In: Physics

In order to pressurize something, it has to be a sealed volume. Consider a balloon. Before you blow it up, it is limp because air can freely move in and out of it. There is nothing to block this movement because the opening is not tied off.

However when you squeeze the balloon’s opening over a tank outlet, what you’re doing is sealing the inside of the balloon off from the outside, and “connecting” it to the interior of the tank. When you open the regulator, gas from inside the tank flows from a high pressure space (the inside of the tank) to a lower pressure space (the outside).

Thing is, the balloon, because you’ve sealed it, “gets in the way.” Effectively what you’re doing with pressurizing is forcing more gas into a volume than it would normally have. The gas from the tank fills the balloon and presses outwards — pressure always wants to equalize, or move from high pressure to low pressure. The skin of the balloon traps this higher pressure gas and prevents it from escaping.

However, we all know what happens when you fill the balloon with too much. The skin of the balloon eventually fails — the internal pressure exceeds the material’s ability to contain it. The balloon then ruptures.

This basic principle is in effect whenever you pressurize something. Beer bottles, tires, planes, etc. Submarines as well, but the pressure gradient is flipped. You take that sealed volume and through means of a pump you force more gas into that volume than you’d normally get.

The most common pressurized stuff that most people used is pneumatic tires used in cars and all types of road vehicles and a lot of other stuff. You pressurize them by forcing air in with a pump sometimes powered by a motor and sometimes by hand.

Airplanes is similar but it is the pressure of the air rundar them that drops but you still uses pumps to force air so the passengers get fresh air.

The pressure in a tire is higher then in the airplane. The atmosphere at sea level is at 14 psi compare to vacuum and the pressure in a aircraft is 11-12 PSI above vacuum and less compare to the air around it. A typical car tire have around 35 PSI over atmospheric pressure So the tire has to hold in over 3 times more pressure then a aircraft.

Even in the vacuum of space you only need 14 PSI to get a sea lever atmosphere so the tire has to handle more pressure then ISS and would not burst if you launched it into space because the pressure only increase to 49 PSI the burst at 200 PSI. You can get 49 PSI a hot day in the sun in a car tire.