How do air compressors work?

Air compressors are essential kit in many jobs, as well as hobbies including DIY – but a lot of people don’t actually know how air compressors work.
In this guide we’ll take a look at how air compressors work, starting with how they produce compressed air, through to how that air is delivered and its use in air powertools.

What is an air compressor?

Let’s start with the basics – what is an air compressor? As the name suggests, it’s a device that takes air from its surroundings at atmospheric pressure, and compresses it to supply output at significantly higher pressure.

You can think of it as ‘pressing’ the air into a smaller space – press, compress and pressure all come from the Latin word ‘premere’ and it’s not hard to see that they have common spellings and meanings.

Parts of an air compressor

A typical air compressor has three essential parts that work in sequence to produce compressed air output.

Drive

Drive is the ‘engine’ of the air compressor. Different air compressors draw their power from different sources. Common examples of this include petrol-driven air compressors and electric air compressors.

The choice of drive can depend on where the air compressor will be used, especially in the case of portable air compressors where there might not always be a mains electricity supply nearby.

Pump

The pump takes the power supplied by the engine or motor, and uses it to compress air. Again there are different methods to do this, such as centrifugal compression, piston-driven compression and rotary screw compressors.

Like the drive method, it’s important to choose the correct kind of pump for the job. So although all compressors need a power source and a pump, the different types of each start to create a long list of different options to choose between.

Tank

Finally, the air compressor needs a tank or receiver to store the compressed air until it is used – it’s unusual and inefficient to connect air powertools or spray guns directly to the compressor output without a receiver.

Receivers are often fitted with extra parts like a dryer or filter, which helps to keep the compressed air output dry and clean, especially for sensitive applications like electronics and pharmaceutical settings.

How air is compressed

The different types of air compressor use slightly different methods to compress the air, but some parts of the process are the same:

  1. Air is drawn into the compression cylinder via an inlet valve. Initially, the air is at normal atmospheric pressure, just like the ambient air surrounding the compressor.
  2. The air compressor uses one of several methods to apply pressure to the air, compacting it into a smaller space at higher internal pressure.
  3. Compressed air is then released into the receiver tank, where it can be drawn through a network of pipes and tubes for use by air powertools and spray guns.

The key part in the process is step two, where the air is compressed from ambient pressure to a much higher pressure, which stores potential energy within it that can drive guns and tools.

Rotary screw compressors force the air along two interwoven screws into a tighter and tighter gap, adding to the pressure in the process – this method is similar to the way a corkscrew pulls the cork out of a bottle of wine.

Centrifugal or radial compressors use a spinning motion to increase the kinetic energy and, in turn, the potential energy of the air. The science here is similar to a fairground Waltzer ride or a salad spinner.

Piston-driven air compressors use a two-stage action. In the first stage, the piston draws back from the chamber, creating a vacuum that sucks in air through the inlet valve. The piston then pushes into the chamber, forcing the air at higher pressure through an outlet valve and into the receiver tank. You may have seen this kind of action in a combustion engine or in the way a syringe delivers an injection.

It’s worth noting that the two-stage process of a piston air compressor means the output is not constant, because some of the time the piston is drawing back instead of applying pressure. However, a receiver tank can help to smooth out the output so there is always compressed air available to use.

What air compressor do I need?

The brief introduction given here should give you some pointers to keep in mind when deciding what air compressor you need for different jobs. For a more detailed guide on air compressors, please head over to the buying guide.

If you’re still not sure, please get in touch and a member of the ACE Compressors team will be happy to help you find an air compressor that’s right for you.

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