An essential tool in many industries, modern style air compressors date back to the 19th Century. But have you ever considered how these machines work?

Direct Air have pulled together data to create this informative graphic to show how these tools provide us with the energy we need for many tasks and have written an in-depth article about how air compressors work.


Oil-free vs. Oil-based Air Compressors

One of the first things you should consider when choosing an air compressor is how it will remain lubricated. All air compressors require lubrication to draw in air to the chamber effectively and safely.

This can be in one of two ways. The first are oil-free air compressors, this uses a non-stick coating within the cylinder, such as Teflon and do not require care or maintenance for this element. They are often cheaper and more lightweight as they use less components.

These oil-free models are more commonly purchased for domestic use. This non-stick coating will eventually wear down after use.

Oil-based air compressors are exactly that, they use oil for their lubrication within the cylinder. They tend to be heavier and more expensive. They also require more frequent maintenance due to the oil needing to be topped up.

They are more robust and tend to have a longer lifespan, they typically are found in industrial use and are commonly used for pneumatic construction tools, dentistry, sanding and blowguns.


Single Phase vs. Dual Phase Compressors A diagram explaining how air compressors work.

These two compressors work in almost the same way. A single-phase draws in air and compresses it, dual-phase has one more step.

The single phase, also known as a piston compressor, draws the air into a cylinder and is compressed by the single movement of the piston using a vacuum system. The air is then sent to a chamber for storage until it is needed.

The dual phase follows these steps but moves the air into an additional chamber to be compressed a second time before storage. Single phase compressors are generally used for home DIY and dual phase for industrial purposes.


Low Noise Air Compressors

A common complaint in relation to air compressors is the noise they generate. Low noise air compressors are available and reduce the decibel rating to roughly 40dB.

This is achieved by having an added acoustic cylinder to contain the noise. Electric-powered air compressors, rather than gas, also generate less noise.


Fixed vs. Variable Air Compressors

The main difference between fixed vs. variable air compressors is how the motor gets its power. Variable speed compressors (also known as VSD and VFD), operate automatically by the motor adjusting speed in accordance with the demand for air.

This is achieved by the power being converted twice, firstly to AC and then to DC with the use of diodes. This means the power can be closely controlled. These are more power efficient, saving money and the environment.

They are initially more costly to purchase, and the repairs and maintenance tend to be higher.

Fixed speed compressors send a continuous stream of power to the motor which gives a reliable frequency.

They are unfortunately less efficient but are cheaper to purchase and maintain but can be more costly to run.


Scroll Compressors

A type of piston compressor, scroll compressors are the most common type of air compressor. The piston travels downwards, which in turn decreases the pressure inside the cylinder.

This sudden pressure change causes the door of the cylinder to force open and pull in air. The piston then travels back up and air is forced out as at higher pressure point.

These models cool down quickly and are more energy-efficient but do come at a higher initial cost.


Rotary Screw Compressors

This works with the same concept as scroll compressors. Instead of a piston, rollers are positioned in the middle of the central shaft with one side always in contact with the wall. These rollers rotate at an extreme speed to obtain the needed pressure.

They have a fantastic power capacity, easy to maintain and a lower cost overall. They do however have limited abilities to cool and require more frequent maintenance checks.



When is comes to choosing the right air compressor, there are many factors to be taken into account. Consider budget, not just for the initial cost but for ongoing maintenance and how much energy this will use.

Also seek an air compressor that is suitable for your most heavy duty tasks and with all we have discussed, you should be able to make an informed choice. Check out for more information.


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