Rotary Screw Compressor Technology Explained

Renowned for their reliability and versatility, screw compressors are the workhorse behind many industrial processes and applications

mobile compressor on tow

How do rotary screw air compressors work?

When it comes to modern industrial machinery, the rotary screw compressor is one of the most widely used technologies. Renowned for their reliability and versatility, screw compressors are the workhorse behind many industrial processes and applications. This durable technology is suited to an array of demanding industry tasks, without which, businesses around the world would encounter operational challenges and efficiency problems.

There are two basic principles of compression in air compressors. One of these is the principle of positive displacement. There are a lot of compressor types that use this method, screw compressors being the most popular.

towable compressor screw rotors
Towable compressor airend - where the compressed air is generated

Operating Principles

As the name suggests, rotary screw compressors use rotary movements to compress the air.  Within the compressor, there is a set of male and female rotors. They will be designed differently so that, when turned in unison, air will become trapped between them. The male rotor has convex lobes and the female rotor has concave cavities; in this way, they can mesh together without touching to achieve compression. Additionally, the male rotor will have slightly less lobes than the female, meaning it will rotate more quickly, effectively driving the female rotor.

Unlike piston compressors which use the same principle of compression, the screw element is not equipped with valves. As such, it can work at a high shaft speed and there are no mechanical or volumetric losses to create imbalance. This means that screw technology can combine a large flow rate with a compact, space-saving design.

Step by Step Screw Operation

  1. An opening valve sucks gas into the compressor chamber. Located in the chamber are the two screw rotors; when the machine is on, they will rotate at high speeds.
  2. As the impellers rotate, they trap and isolate air in the cavities between the rotors, thus moving the air down the chamber.
  3. The chamber decreases in size and is moved away from the opening valve. As the volume decreases, the pressure increases.
  4. Pressurisation builds and thus the air is condensed.
  5. Air pressure will trigger the compressor’s discharge valve to open, allowing the pressurised air to enter a receiver or other holding tank.
  6. Air is compressed and can be transferred to downstream equipment such as dryers and oil/water separators for drying and contamination removal.

Watch the video to see this process in action:

What are the benefits of rotary screw air compressors?

As the technology of choice across a wide range of applications, screw compressors have a lot to offer customers:

Continuous operation - Capable of continuous airflow and pressurisation, they don’t need to be shut on and off and have no duty cycle. This means that they can operate continuously with little to no downtime. 

Easy to maintain - With very little moving and contacting parts, wear and tear are minimised. Long service intervals drive down maintenance costs and make any routine checks and repairs quick, easy, and hassle-free.

Powerful performance - Screw compressors can operate in challenging conditions as they have high airflow rates and can perform at extreme temperatures. This means they can run pneumatic tools and heavy equipment easily and efficiently.

Energy-efficient - Having stood the test of time, these durable machines produce less heat and conserve more energy than other models. These design features mean that they offer zero loss of capacity over time, keeping the lifetime cost of the compressor low.

Low noise - Quiet operation is down to the small size of the units and the lack of moving parts, making them suitable for point of use installations. 



Oil lubricated screw models

Sometimes called flooded or oil-injected rotary screw, oil-lubricated compressors use lubricant within the compression chamber to cool and lubricate the compressor element. The lubricant helps to form a seal and also has a great noise-damping effect.

Oil-lubricated compressors are reliable, hardy, and efficient, making them suitable for a variety of production processes. Downstream equipment such as oil filters and dryers can remove any oil contamination from the end product, creating a clean compressed air flow suitable for building work, waste management, quarrying, recycling and many other uses.

CompAir design and manufacture a complete range of lubricated screw air compressors from 2 to 250 kW with airflows from 0.24 to 47 m3/min and pressure ranges from 5 to 13 bar.


oil-free compressors family image

Oil-free screw models

Oil-free compressors do not use any oil in the compression chamber, effectively removing the risk of contamination. When air purity is mission-critical for your business and even the smallest amount of contaminant could cause disruption to your process, even spoiling the end product, oil-free models offer peace of mind. For contaminant free air, trust oil-free screw compressors.

CompAir’s Ultima offers ISO-8573-1 Class Zero certified clean air, guaranteed. Ultima utilises low and high pressure dry screw airends which are individually driven by variable speed motors to offer unrivalled levels of energy efficiency. The ground-breaking design is compact, space-saving, and doesn’t compromise on performance. In fact, it offers a footprint 37% smaller than a conventional two-stage oil-free compressor!

Other products in our oil-free range include the DH series of water-injected screw compressors which offers 100% air purity to customers. In this model, high-quality water is used to lubricate, cool, and seal the compressor as a replacement for oil. By removing oil from the process entirely, you can guarantee a dry air output perfect for an array of stringent industries such as chemical, pharmaceutical, and food and beverage. For applications where compressed air comes directly into contact with the product, the DH series is a fantastic choice.

Another choice is the D series of fixed and regulated speed rotary screw dry compressors. These two-stage models have been designed to offer safe and reliable operation in the most demanding situations. Delivering state-of-the-art performance with low life cycle costs, the D series is a fantastic addition to any industrial compressor installation.

Suitable for a variety of applications and industries

Many businesses rely on screw compressors for their everyday production capacity. They are highly suited to heavy-duty industrial operations due to their lack of a duty cycle and their robust design. Common industries where screw air systems support you are manufacturing sectors such as automotive, brewing, food packaging, aerospace, construction, and more. They are ideal for both small and large scale operations as they can handle a wide variety of operating conditions, making them the perfect choice for many professionals.

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