Different Types of Air Compressors and Their Uses

The principle behind air compressors is simple. Air is drawn through the intake, then compressed into a smaller volume at higher pressure for distribution through the compressed air system.

However, several technologies are used to compress that air. Understanding those technologies and the different types of air compressors that use them can help you find the best compressor for your operations.

Positive displacement vs dynamic compressors

Air compressors fall into two main categories: positive displacement and dynamic displacement.

When most people think of air compressors, even if they know nothing about them, they imagine a positive displacement compressor where the air is trapped, then squeezed, and the compressed air is discharged.

Dynamic compressors work by accelerating the air to a high velocity, then slowing it to convert the kinetic energy into pressure.

Positive displacement compressors

The main types of positive displacement compressors are piston, rotary screw, scroll, and rotary vane compressors.

Piston compressors: often known as reciprocating compressors, these feature pistons on a camshaft that draw in and compress air. Compact and affordable, they are frequently used in workshops and garages. However, they tend to be noisy and are not as energy efficient as other types, meaning they are best for situations that only need occasional compressed air.
Rotary screw compressors: two interlaced screws turn in opposite directions, forcing trapped air into a smaller and smaller volume. Rotary screw air compressors tend to be quiet and cool running, making them suitable for continuous operation. Their design reduces maintenance needs. They are the most common industrial air compressors.
Scroll compressors: a scroll air compressor works similarly to a rotary screw compressor, trapping air between a stationary and moving spiral in the compression chamber. As the scroll moves, the air volume is reduced, creating pressure. Like screw compressors, they are quiet and low maintenance but are not well-suited to high volume uses.
Rotary vane compressors: rotary vane compressors use vanes mounted on a rotor that create cavities. The rotor is offset in the chamber so that as it rotates, the cavities reduce in volume and compress the trapped air.

Dynamic displacement compressors

Centrifugal and axial air compressors both use dynamic displacement.

Axial air compressors: perhaps the rarest type of compressors used in industry, axial air compressors use rows of rotating and stationary blades to generate pressure. Complex and expensive, an axial compressor can generate very high airflow rates, but the pressures are relatively low.
Centrifugal air compressors: high-speed impellers push air around at high velocities, then diffusers slow the air, converting the kinetic energy to air pressure. Centrifugal compressors can generate high volumes of air at high pressures. However, they become increasingly inefficient with low loads, so they are most commonly seen in large operations.

Oil vs oil-free air compressors

Air compressors can also be categorised as oil-lubricated and oil-free. These do not refer to the method of compressing air, but instead whether oil is used in the compression chamber.

Uses that require the highest, class 0, air quality, like food processing, pharmaceutical, and electronics, will need oil-free compressors. Oil-free variants are most common with rotary screw, scroll, and centrifugal air compressors.

Oil-lubricated compressors can still generate highly pure air, but cannot guarantee entirely oil-free air, even with extensive filtering. However, by using oil, they tend to have better cooling and reduced wear and tear.

Different Types of Air Compressors and Their Uses

Choosing between the types

The range of air compressors can make the choice seem difficult. However, the benefit is that there is probably a compressor that is perfect for your needs.

There are several factors that you will need to consider.

Airflow requirements: the amount of air you require is a key factor; usually measured in cubic feet per minute (CFM), you must ensure the compressor can cover your needs.
Pressure: your tools will need specific pressure for optimal operation. You must ensure your compressor meets those requirements.
Duty cycle: some compressors, like rotary screw compressors, are designed for continuous use. Others have a duty cycle, which is expressed as a percentage of the time they can operate. Your use case may mean specific types of compressors are more suitable.
Working environment: the location and positioning of your air compressor can dictate your choice. For example, a large centrifugal compressor may be impossible if you have a small site. But you will also need to consider things like the operations around it and issues like noise and heat generation from the compressor if staff are nearby.
Energy consumption: air compressors are cost effective, but you may want to consider how to minimise costs. Ensuring your air compressor has a high-quality air intake or integrating heat recovery, for example, can help reduce your bills.
Compressed air use: what you need compressed air for may determine your choice. For example, a piston compressor will suffice if you are occasionally powering a single pneumatic tool. If running a major pharmaceutical production line, you must consider oil-free options, potentially those designed for continuous operation.

Choosing the right air compressor

Investing in the right type of compressor ensures lower running costs, higher efficiencies, and increased productivity. Getting that choice right can be difficult if, like most users, multiple types of compressors meet your criteria.

We have been serving the region’s compressed air needs since the 1950s, and as an employee-owned business, every member of the Search Air team is dedicated to one thing: giving you the best possible service.

Whatever your situation or needs, get in touch. From designing and installing a complete compressed air system from the award-winning range of Atlas Copco compressors, to providing you with our unobtrusive servicing to keep your existing compressor in the best possible shape, we are here to help.