Why are gases easy to compress?

Using compressed air? Wondering how it works? We turn science into easily understood explanations for why gases are easy to compress.

Estimated time to read: 4 minutes

January 18, 2024

Solid, liquid or gas?

Is the world flat? Are men better at reading maps? Does Bigfoot exist? There are loads of questionable theories you might subscribe to that we would prefer not to go into. But we fully support the school science teacher who taught you there are three different states of matter: solid, liquid and gas. And we will even support them when they say that gases are easy to compress.


We also know that time and memory don’t always mix, and that you may be wondering why gases can be compressed. We explain the basics.

Why gases are easy to compress

When you have a solid, the tiny little molecules that make it up are very close together. Think of ice. It’s very hard to move your hand through a big block of ice. You could sit on top of a huge sheet of solid ice and not fall through it.


But let’s imagine the ice is in a liquid state—water. You would be able to move your hand through it pretty comfortably. This is because the tiny water molecules are further apart. However, they’re still close enough together to be able to support you when you swim, surf or drop or float an oil tanker on the top of them. When you turn the water into steam, the molecules are even further apart. In fact, they’re so far apart that they’re unable to support any weight at all. Your surfboard would fall straight through them. 


It’s this space between the molecules that makes compression possible. You’re theoretically able to compress steam, or any other gas such as air or oxygen. 


You could try to compress solids and liquids. However, the molecules are so close together that it doesn’t really make much difference to the actual volume.

Can gas be compressed into a liquid or solid?

Yes. Gases turn into liquids and even solids if enough pressure is applied. Depending on the type of gas, it takes an incredible amount of pressure to pull it off, more than an air compressor produces. And it generally requires a cooler temperature than room temperature. Unfortunately, when you compress air in an air compressor, you typically end up raising the temperature. And so, it’s not possible to compress air to the extent that it turns into a liquid.


But you do (kind of) do this with water. 


How? When you compress air, everything in the air is compressed. This includes moisture, condensate or, in simple terms, water vapour. The little molecules are too small for you to see. They’re entirely absorbed in the gaseous air. 


When you turn it on, your air compressor takes in atmospheric gaseous air and compresses it. This means that while compressing the atmospheric air, it compresses the water molecules that are in the atmospheric air. They’re pushed together.


Although the air and the water molecules are being heated during the compression process, they do eventually cool. And this means that the heavier water molecules are going to fall through the lighter matter such as oxygen and nitrogen, to band together as liquid water or condensation. Voila! You’ve basically turned water vapour into liquid water. 


You’ll also understand why you have an air dryer—most likely arefrigerated dryer or an adsorption dryer—attached to your compressor. And when you think about the way that other nasties in the air—such as oil—are compressed and cooled as well, it’s clear why there are all kinds of other filters involved in removing them.

More info on why gases are easy to compress

Would you like to know more about why gases are easy to compress? Or why there is water or condensation in your compressed air? Do you have any other question about compressed air and air compressors? We are more than happy to answer them! Get in touch with us. We are always happy to help.

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