How An Air Compressor Works

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Air/pneumatic tools will use an air compressor as their power source, instead of using electricity, and offer many benefits when completing DIY projects. With so many tools now available on the market that use pneumatic (or air) power, it is important to know how an air compressor actually works! Keep reading to find out exactly how an air compressor works, which will hopefully help you if you are in the market for one at the moment. 

Want to know more about air compressors, why not check out our air compressor buyers guide.

Compressor Parts

There are some main parts of a compressor that you will need to know to be able to understand exactly how these clever machines work. 

  • Inlet and discharge valves – The inlet valve will suck in the air ready to be compressed, whereas the discharge valve will expel the air once it has been compressed. 
  • Reciprocating piston – Used to create a vacuum which sucks in air and then compresses this air when it moves back. 
  • Crankshaft – Part of the mechanism that is used to move the piston forwards and backwards in the cylinder. 
  • Air tank – Used to store air at certain pressures until you and your pneumatic tool need it! 

How Do Air Compressors Work?

Most air compressors will be powered by electric motors (although some larger models are powered by gas). The purpose of the compressor is to convert this electrical energy into kinetic energy, to power more efficient, lighter and safer tools. 

There are two main types of air compressor, which both work in different ways.

Positive-displacement compressor 

Positive-displacement is the main way in which air compressors work. The pressure of the air is increased by reducing the space that the air is in. A crankshank controls the reciprocating piston moving it back and forwards, allowing more air in and then compressing this. When the piston moves down, a vacuum is created in the machine (allowing air to flow in through the inlet valve). Then, when the piston moves back up this air is compressed against this inlet valve (which closes it and stops the air from just leaving the device). This air can then be forced into an air tank (in most average to large models) where it is stored at high pressure until you are ready to use it. 

Rotating impellers (Rotary Screw Air Compressor)

Rotary air compressors work in a slightly different way to positive-displacement compressors and are less common. They work by a rotating type of “fan” or helical screw that contains the air between the wall of the container. As the volume of the area is decreased the air is compressed and then travels into a different part of the tank. 

What happens next?

After the air has been pressurised and stored in the air tank, the process continues until the pressure inside the tank has reached capacity (this varies for different models and is usually measured in PSI). At this point, the air compressor will switch off until it senses the pressure dropping below the maximum PSI – at which point it will switch on again. This process continues for as long as you are sending power to your air compressor, so that – providing your air compressor is powerful enough for your tools – you will have a constant stream of kinetic energy for your tools. 

REMEMBER: Different tools will have different maximum pressures that they are able to work with – too little will stop the tools working effectively, too much will damage the tool. Air compressors will have valves that allow you to set your desired pressure, and make sure that the PSI is maintained at this while working with your tool using a regulator to check the pressure inside the tank. 

How Air Compressors Work

Oil-lubricated and Oil-free Air Compressors

You will find that there are both oil-lubricated and oil-free air compressors available on the market – both of which work in rather different ways. 

Oil-free air compressors will usually be lighter and cheaper than oil-lubricated models, but they will also heat up sooner and tend to have a shorter life span. When purchased they will come with lasting lubrication so need a lot less maintenance, but you can find that a certain level of moisture from the vapour in the air will build up in the machine, which can cause damage over time. 

Oil-lubricated air compressors work by splashing oil onto the walls and bearings of the compressor tank, which keeps the machine running smoothly and much cooler, especially if it is being asked to work for any great 

Want to know more about air compressors, why not check out our air compressor buyers guide.

Frequently Asked Questions

What is the difference between 1-stage and 2-stage compressors?
A one-stage compressor will work using one piston pump to draw air into the cylinder and to increase the pressure by compressing the air. Whereas a two-stage compressor will use one piston to pump air into another cylinder, where the air is compressed using a different pump. 2 stage air compressor tends to be used for larger or industrial compressors that need to be able to work faster and compress more air for the tools that they are powering. 

What does CFM stand for?
CFM stands for cubic feet per minute, which is the amount of air that an air compressor can compress each minute. The more air that can be compressed, the longer the machine will be able to work and power your tools before it needs time to compress more air (it may even be able to work continuously). It is worth mentioning however that the machine will be affected by the heat, humidity and the wind surrounding it, as this will affect how much air can be sucked into the vacuum in the first place! 

What are dual-piston compressors?
A dual-piston compressor has two pistons, which means the air compressor will have two strokes per revolution instead of one. This means that double the air can be sucked into the vacuum and compacted together to increase the pressure per revolution. The only time this is different is when the two pistons are used to create a 2-stage air compressor (see above).

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About Mike Jones 178 Articles
I started doing DIY around the house and it soon developed into a hobby. I look for tools and products that are genuinely useful and get the job done. I enjoy writing product reviews, researching my buyers guides and putting tools through their paces. In my downtime, I like to run and I am a bit of a Netflix documentary geek.

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