Why are gases easy to compress? The ins and outs of air compression

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You might already be aware of all the different types of air compression. You’ll also know that air compressors are used in many industrial applications. But what about the science of air compression? How does air compression work exactly, and why are gases so easy to compress. We’ll answer these questions and others in this article.

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Why are gases easy to compress?

So what makes gases easy to compress, as opposed to other types of matter? We’ll explain. 

On earth, we have three different types of matter: 

  • solids, like dirt, wood and stone;

  • liquids, like water and oil;

  • gases, like oxygen or hydrogen.

From these three types of matter, gases are the only ones that can effectively be compressed. But why are gases easy to compress as opposed to liquids or solids? 

The simple answer: because there is lots of space between gas molecules. This space allows us to put pressure on gas, and force it in a smaller container. 

Take a scuba tank for instance: they typically contain 10 liters of gas (more specifically: oxygen), because the pressure is about 200-300 atmospheres. If the pressure would be decreased to the regular 1 atmosphere, you’d need a tank of about 2500 liters to contain the oxygen. So it’s the space between molecules that makes compression possible.

If you’d apply the same pressure to solids or liquids, there wouldn’t be a change in volume. The molecules of liquids and solids are too close together already: there isn’t any space left to decrease. Therefore compression isn’t possible.

What happens when air is compressed?

Let’s talk more about air compression. We’ve already offered you an introduction to compressed air in our article ‘What is compressed air, how can it be useful?’. 

But what exactly happens in an air compressor?

Firstly, you should know that an air compressor takes the ambient air to start compressing. They don’t use pure oxygen like applications for scuba diving or hospitals do. This means that every particle that is present in the ambient air will also be present in the compressed air. 

For instance: if there’s water vapor in the air (which is most certainly always the case) the compressed air will also contain water vapor. If you’re using an oil-lubrication system, the compressed air will also contain small amounts of oil. Depending on the end-use of the air and pollution regulations you’ll need an air dryer and/or oil filter to remove these particles from the compressed air in a later stage. 

So what happens when air is compressed? 

Your air compressor needs input power to work. The power that is supplied is then completely converted into heat. This means that the heat production of your air compressor is equal to the input power. So make no mistake: air compressors do generate lots of heat. In lots of cases it’s advisable to reuse this heat, for example to power the local heating system. That way you won’t lose unnecessary energy. 

The aforementioned water vapor is also an integral part of air compression. The amount of condensate vapor depends on these factors: 

  • the amount of vapor in the ambient air;

  • the amount of compressed air in general;

  • the drop in temperature after compression;
  • the general air pressure during compression.

Do you have more questions on compressed air?

We’re always happy to answer any questions you may have about air compressors and the uses of compressed air. Just let us know and we’ll get back to you as soon as possible.

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What air compressor do I need?

If you’re still not sure what type of air compressor you need, feel free to get in touch with our experts for personal advice. We’ll assess your situation and help you find the perfect compressor.

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