Air Supply UK: Specialist Compressed Air Engineers

Published: 14/03/2022

How does a rotary screw air compressor work? 

Rotary screw compressors are one of the most popular types of air compressor in industrial applications where larger volumes of compressed air are required. These compressors supply production processes in industry, trade and workshop applications to provide a reliable supply of high quality compressed air. 

What is a rotary screw air compressor? 

Traditionally, air compressors have been reciprocating air compressors, or piston air compressors. These compressors use pistons to push air into a smaller space, which compresses it. This compressed air is then collected in an air receiver tank. Rotary screw compressors are a newer, improved type of air compressor that are more complex, efficient and flexible than reciprocating air compressors. 

Rotary screw air compressors use a rotary positive displacement mechanism which is made up of two gears (screws) which rotate to compress air by reducing the volume of the chamber. 

The rotary screw compressor is one of the most widely used technologies in modern industrial machinery. They are chosen for their reliability and versatility and used across many industrial processes and applications. 

The key difference between a rotary screw air compressor and a reciprocating air compressor is that they deliver a constant (non-pulsating) stream of compressed air and are 100% duty cycle machines. 

Unlike piston compressors, screw compressors have no valves or mechanical forces that can cause unbalance. As a result, screw compressors can operate at high speeds and provide a high flow rate. 

The most common applications of rotary screw air compressors are continuous, workplace and industrial applications. There are two different types of rotary screw air compressors: oil free and oil injected. 

How do rotary screw air compressors work? 

The basic principle of a screw compressor is a male rotor and female rotor which spin in opposite directions. The air is trapped between the two rotors which reduces the volume of the trapped air as it moves through the rotors. This reduction in volume results in compressed air which can then be used to power air tools and more. 

A series of filters separate unwanted moisture and residue from the compressed air as it exits the machine from the outlet. 

Screw air compressor working principle 

The step by step of a rotary screw air compression process is as follows: 

Step one: The opening valve sucks gas into a compressor chamber. Inside the chamber there are two screw rotors which rotate at high speeds when the compressor is turned on. 

Step two: As the rotors rotate, they trap and isolate air in the cavities between the rotors, which moves the air down the chamber. 

Step three: The chamber decreases in size and is moved away from the opening valve. As the volume in the chamber decreases, the pressure increases. 

Step four: Pressurisation in the chamber builds which condenses the air further. 

Step five: This pressurisation will trigger the compressor’s discharge valve to open, allowing the pressurised air to enter a receiver or a holding tank. 

Step six: The air is compressed and can be transferred to the right tools. 

Types of rotary screw air compressor 

There are two different types of rotary screw air compressor: 

Oil lubricated rotary screw compressors 

Also referred to as a flooded or oil injected rotary screw compressors, oil lubricated compressors use lubricant within the compression chamber to cool and lubricate the compressor element. The lubricant helps to form a seal and provides a noise dampening effect too. 

These compressors are reliable, hardy and efficient which makes them suitable for a number of production processes. Oil filters and dryers help to remove oil contamination from the finished product which provides compressed air which is suitable for building work, waste management, quarrying, recycling and more uses. However, for applications where oil contamination can be an issue, this type of compressor is not suitable. 

Oil free rotary screw compressors 

Oil free screw compressors do not use oil in the compression chamber which means that there is less risk for oil contamination. When air purity is essential for the business this is the best type of air compressor to choose. For some applications, even a small amount of contamination could cause disruption to the process and spoil the end product, so oil free air compressors offer peace of mind. 

A huge number of businesses rely on screw compressors for everyday production capacity. They are highly suited to heavy duty industrial applications such as automotive, brewing, food packaging, aerospace, construction and more. Rotary screw compressors are perfect for both large and small scale operations, making them the perfect choice for a number of applications. 

If you’d like more information on what a rotary screw air compressor is or which compressor to choose for your application, please contact our expert team.

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