An Introduction to Compressed Air

Compressed air is used all around us in everyday life. It can be used in the form of blowing air or as an energy source and it is used to power or produce many of the things we use. From opening a bottle of fizzy drink, riding a roller coaster, taking the bus, visiting the dentist or the electricity we use each day, compressed air will have played a role in each one of these experiences.

compressed air for industry

What is compressed air?

Compressed air is air that is pressurised to greater than atmospheric pressure. It is exactly the same as the air that you breathe only it has been forced to a smaller volume and kept under pressure. Air is made up of 78% nitrogen, 20-21% oxygen and around 1-2% of other gases as well as water vapour. When compressed, the air is still made up of the same mixture of gases, however, it will have been forced into a smaller space, bringing the molecules closer together.

Compressed air can be stored at a high pressure and is a fantastic medium for transmitting energy. Compressed air is a popular energy source as it is safer and easier than alternative options like steam and batteries. Steam can be dangerous as it gets extremely hot whereas batteries can run out of charge, making both options unfavorable.

Compressed air is safe to use, easy to store and has many versatile uses.

rotary screw compression method
The highlighted section shows air being compressed

How is air compressed?

Air is compressed by air compressors. Air compressors draw in air at an inlet valve, they then compress the air to the required volume and release the pressurised air through the discharge valve into a storage tank. The compression process is usually powered by an electric motor.

There are two types of air displacement which a compressed air system may operate upon:

Positive Displacement - The most common compression method, positive displacement compressors force air into a confined space, usually through the movement of a mechanical device.

Dynamic Displacement - Compared to positive displacement compressors which physically reduce the volume of captured air, dynamic displacement compressors speed up the air to high velocity. The energy created from this builds up air pressure.

Positive displacement technologies

Positive displacement compressors use various technologies to compress air, they fall into two main categories: rotary and reciprocating. Rotary compressors use a rotating component to compress gases whilst reciprocating compressors use a piston cylinder to pressurise air as it moves up and down in a reciprocating motion.

Main types of rotary compressor


Rotary screw compressors use two meshed rotors which rotate together and force the air down the rotors, compressing it to a higher volume. Watch this simulation of the CompAir L series rotary screw compressor showing the main components of the compressor in action.


Rotary scroll compressors use two interweaving scrolls to pump and pressurise the air. Often one of the scrolls will be fixed while the other orbits it, thus trapping and compressing pockets of air.


Rotary vane compressors use a rotor with a number of blade-shaped vanes inserted in radial slots in the rotor. As it rotates, the centrifugal motion compresses the air.

Main types of reciprocating compressor

compair v compact piston compressor

Operating in the same way as internal combustion engines, reciprocating piston compressors use a crankshaft with a connecting rod and piston. The piston is driven by the crankshaft which moves inside a cylinder to deliver gases at high pressure.

This example on the left shows a typical example where air is compressed in stages, the 1 stage on the right hand side compresses air up to a given pressure, this pressurised air is then injected into the 2nd stage on the left hand side with a smaller piston diameter to further compress the air to an even higher pressure. This would be used to fill air tanks for scuba divers and fire and rescue services who use breathing air.

Where is compressed air used?

Compressed air is used as an energy source and as active air.

As an energy source compressed air is often used to power pneumatic machinery such as drills, hammers, wrenches and grinders.

Active air is air that comes directly into contact with the product. For this reason, it must be clean, dry and contaminant free. To ensure these standards are met, many choose to use oil-free air compressors or air tools to help clean and dry the compressed air.

Some of the core industries that use compressed air include:

Manufacturers of chemicals will want to ensure the quality of the products they deliver. Due to the unstable nature of chemicals, it is important that the compressed air used is clean and oil-free. Uses within this industry include material handling, air curtains and product drying.

Compressed air plays an integral role in the production and manufacture of cars. From assembly using air-operated robots to the finishing coat of paint using compressed air spraying tools, the automotive industry relies on compressors to produce high-quality vehicles.

Compressed air is used widely in industrial applications including for construction jobs, mechanical repairs jobs, road maintenance, factory manufacture, production lines and many industrial processes.

Food & Beverage
Since any food or drink product must be fit for human consumption, any active air that comes into contact with it must meet stringent health and safety standards. Within this industry, some of the common uses include air knives, product handling, food filling machines, packaging and fluid pumps.

Pharmaceutical companies rely on compressed air for process air used for cleaning, aeration and product moving as well as for packaging medication. Due to the high health and safety standards surrounding pharmaceuticals, a sterile environment must always be maintained. Compressed air used within this industry must be completely clean and contaminant free.

Oil-free is the predominant compressor type used in heathcare, pharmaceutical and laboratory operations and the food and beverage industry.

oilfree compressor for healthcare and pharmaceutical

Compressed Air Quality

The end quality of the output air is a very important factor to consider when choosing an air compressor. There are different air purity classes laid out by the International Organisation for Standardisation (ISO) that govern what constitutes clean air.

ISO Class 1
This standard lays out criteria and limitations for how much contamination and oil content can be within the air output. Although Class 1 standards require a very tiny percentage of oil and can be classed as ‘technically’ oil-free, it is not the cleanest standard of air available.

ISO Class 0
Class 0 air quality guarantees 100% air purity. This new class was brought into existence to meet the growing demands for sterile air within the industry. It is the cleanest choice available and is highly recommended for applications where air purity is critical.

What are the benefits of using compressed air?
Compressed air is trusted by millions across the world every-day. Some of the main benefits of using compressed air are:

* It is safe and easy to use
* It improves productivity
* It's a cheap and energy-efficient power source
* It offers low operating costs
* It's versatile

The Fourth Utility
Alongside electricity, gas and water, compressed air is often considered to be the fourth utility in the industrial and manufacturing world. Many businesses, small or large, rely on compressed air to power essential processes for their application. It plays an extremely vital role in powering most aspects of the modern world.

The core thing that makes air compressors so popular compared to other power sources is that people can generate their own compressed air on-site. Plus, air compressors can be configured with a variety of accessories to meet the demands of the industry entirely, producing a specific quality, pressure and flow to suit unique needs.

compressed air - the fourth utility