Published: 05/04/2022
Rotary Screw Air Compressors: How Do They Work and Why Should I Buy One?
A rotary screw air compressor compresses air using two interlocking helical rotors (screws) that spin in opposite directions, trapping air and reducing its volume to increase pressure. Because there are no pistons or valves, screw compressors deliver a constant, non-pulsating stream of compressed air at 100% duty cycle, making them ideal for continuous industrial use. A typical unit lasts 60,000–80,000 running hours.
What is a rotary screw air compressor?
A rotary screw air compressor uses two interlocking screw-shaped rotors to draw in and compress air. Some of its most common applications are in factories, where a steady supply of compressed air is needed.
Unlike a traditional piston air compressor, a rotary screw compressor doesn’t rely on pistons or valves to compress air. Instead, it uses two rotating screws to create a continuous flow. This design minimises vibration, making it suitable for quieter environments such as hospitals and other medical environments.
And the good news is that they require less maintenance. Rotary screw air compressors can run for long periods without needing to stop and cool down, making them a preferred choice for high air demands.
How Does a Rotary Screw Air Compressor Work?
A rotary screw air compressor works by drawing air into a chamber, as two interlocking screw-shaped rotors spin in opposite directions. As the rotors spin, they trap the air and move it gradually through the chamber. The space between the rotors gradually becomes smaller, squeezing the air into a smaller volume. In turn, this increases its pressure. Once compressed, the air passes through filters to remove moisture and particulates, and is then delivered to air tools.
How the compression process works:
- Air is drawn in: The process begins when the compressor pulls air into the compression chamber through the inlet valve.
- The air is trapped: As the two rotors rotate, they trap pockets of air between the screws.
- The air is compressed: The trapped air is carried along the length of the rotors. As the space between the screws gets smaller, the air is compressed and its pressure increases.
- The compressed air is released: Once the air reaches the required pressure, it exits through the discharge port.
- The air is ready to use: Before reaching your equipment, the compressed air passes through filters and separators that remove excess moisture and other contaminants. It’s finally ready to use via air tools and other equipment.
The compression process is one of the main reasons rotary screw compressors are so efficient. Unlike piston compressors, they don’t need to repeatedly start and stop. Therefore, businesses choose this compressor type if they require a constant air supply.
Types of Rotary Screw Air Compressors
There are two types of rotary screw air compressors available on the market: oil-injected and oil-free. While they both work in the same way, the key difference is whether oil is used during the compression process. The right option depends on the level of air purity your application requires.
Oil-Injected (Oil-Lubricated) Rotary Screw Compressors
Oil-injected rotary screw compressors are the most widely used type across industry. They introduce oil into the compression chamber to lubricate the rotors. The oil also plays an important role in cooling the compressor during operation, helping it run more efficiently.
- Best suited for: Heavy-duty environments such as construction sites, waste management facilities and recycling operations where a small amount of oil carryover is acceptable, and not against production laws.
Oil-Free Rotary Screw Compressors
Oil-free rotary screw compressors are designed without oil in the compression chamber. Therefore, you’ll find them in more sensitive industries where quality oil-free air is critical.
- Best suited for: Industries where clean, oil-free air is essential, including food production, pharmaceutical manufacturing, medical environments and automotive paint finishing.
Advantages of Rotary Screw Air Compressors
Long service life
With regular maintenance, a rotary screw compressor can often achieve around 60,000 to 80,000 hours of operation. This is up to four times longer than other compressor types on the market.
Quiet operation
As rotary screw compressors don’t use pistons, they run much more quietly than traditional piston compressors. This makes them a popular choice for industries where noise levels can be a cause of concern.
100% duty cycle
Built for demanding working environments, rotary screw compressors can deliver a consistent supply of compressed air for long periods without the need for frequent stops.
Energy efficient
Rotary screw compressors are designed to use energy efficiently by reducing heat loss. Their efficient operation can reduce running costs and minimise the environmental impact that businesses generate each year.
Clean, dry air
The rotor system manages lubrication, which minimises contamination in the compressed air.
Is a Rotary Screw Air Compressor Right for Your Business?
A rotary screw air compressor is the right investment if your business needs a continuous supply of compressed air. It’s most commonly used in manufacturing, automotive workshops and heavy industry. On the other hand, if your air demand is lighter or intermittent, a piston compressor may be a more cost-effective option.
To be on the safe side, it may be worth contacting an expert such as Air Supply UK to inspect your site and determine the best compressor type for your needs. We stock new rotary screw compressors and also offer one of the UK’s largest ranges of quality used air compressors, backed by expert servicing and repair.
At Air Supply, we provide regular servicing and our reliable team of service technicians can help you make sure your compressor is kept in the best condition.
If you’re interested in buying a rotary screw air compressor, you can take a look at our rotary screw air compressors online. Or, if you’re working to a lighter budget, check out our large variety of used air compressors.
Contact our expert team for tailored advice on the right compressor for your application.
Frequently Asked Questions
How long does a rotary screw air compressor last?
With regular servicing and ongoing maintenance, a rotary screw air compressor can typically provide 60,000 to 80,000 hours of operation. This is much longer than many piston compressors, making them a strong long-term investment for businesses that rely on compressor air daily.
What is the difference between a rotary screw and a piston air compressor?
A rotary screw compressor uses two rotating helical screws to compress air, which delivers a constant, non-pulsating airflow at 100% duty cycle. They’re best-suited to continuous industrial demand.
On the other hand, a piston (reciprocating) compressor uses pistons and valves to operate, meaning it causes more noise than a rotary screw compressor. This type of compressor is best suited to jobs where compressed air is only needed occasionally. Unlike rotary screw compressors, they’re not designed for long periods of continuous operation. They typically require breaks between uses to prevent overheating.
Are rotary screw compressors oil-free?
They can be. Oil-injected models use oil in the compression chamber for cooling and lubrication, while oil-free rotary screw compressors keep oil out of the chamber entirely.
Can a rotary screw compressor run continuously?
Yes. Rotary screw air compressors are designed for a 100% duty cycle that allows them to run constantly throughout the working day. Unlike piston compressors, they don’t need regular breaks to cool down. This is because their smooth rotary design helps maintain lower operating temperatures, reducing the risk of overheating.