How to Choose the Right Rotary Screw Compressor?

Rotary screw compressors are vital in various industries, offering efficient, reliable compressed air. But there are countless applications and many different types of rotary screw air compressors. Selecting the right one for your business can be a daunting task given the variety of options available.

Whether you're in manufacturing, pharmaceuticals, or construction, understanding the key features of these compressors can help you choose the best one for your application. This guide aims to simplify the process, drawing on Atlas Copco's extensive experience in compressed air systems.

What is a rotary screw compressor?

A rotary screw compressor uses two rotors (helical screws) to compress air, differing significantly from reciprocating air compressors which utilize pistons. As the screws interlock, they reduce the volume of air, increasing its pressure. This design allows for continuous operation, making rotary screw compressors ideal for applications requiring a constant air supply.

Their benefits? In addition to the efficiency, reliability and versatility, rotary screw air compressors have many other advantages: 

• Their noise output is low and their physical footprint small. That means you can install them in more places.
• Unlike piston compressors, they don’t need cool-down periods. This allows them to operate continuously and they do not require a lot of maintenance. 
• In addition, oil-lubricated rotary screw compressors feature a low oil carry-over of as little as 3 ppm.
• Finally, over their expected service life of 10 years or more, you don’t have to worry about a loss of capacity. 

How to choose the rotary screw compressor that fits your facility?

Oil-free and oil-injected rotary screw compressors

First of all, it is essential to determine whether an oil-free or oil-injected rotary screw compressor best suits your requirements. Choosing between oil-free and oil-injected rotary screw compressors depends on your air purity requirements. Oil-free compressors provide high-quality air, which is essential for industries like food processing and pharmaceuticals. Oil-injected models are more common and cost-effective, suitable for general industrial use where air purity is less critical.

Two drive types, lots of benefits

Now that you've already selected between an oil-injected and an oil-free compressor, the next step is to choose the drive type for your air compressor. Atlas Copco offers rotary screw compressors with belt or gear drives. Belt-driven compressors are cost-effective and easy to install, operate and maintain, ideal for smaller operations. Gear-driven models are quieter and more efficient, suitable for larger, more demanding applications. Their initial investment cost is a little higher. However, because they are more efficient and maintenance free, compressors with gears are less expensive to operate. This will allow you to quickly recoup that higher cost. 

Fixed-speed, dual-speed, and variable speed rotary screw compressors

Fixed-speed, dual-speed, and variable-speed rotary screw compressors are the common options for various applications. 

It is often said the choice between fixed-speed and variable-speed rotary screw air compressors typically depends on your air demand. Fixed-speed compressors run at a constant speed, best suited for applications with steady demand. Variable speed drive (VSD) compressors only when you have fluctuating demand.

Despite such common perceptions, fixed-speed compressors aren't necessarily the ideal choice for constant air demand. VSD compressors are also perfectly capable of handling such scenarios by dynamically adjusting their speed to match air demand, delivering higher efficiency and energy savings for both stable and fluctuating needs. Ultimately, the decision boils down to budget constraints rather than specific application requirements. 

A third option exists, offering greater energy efficiency than fixed-speed compressors at a lower investment cost than VSD compressors. Dual-speed technology optimizes free air delivery at any given pressure setting. While it requires a higher initial investment compared to fixed speed, it offers increased flexibility and is well-suited for applications requiring high flow at various pressures. 

In conclusion, when considering fixed-speed, dual-speed, and variable-speed rotary screw compressors, a VSD compressor emerges as the superior choice for applications with both variable and steady demand. Its efficiency benefits not only your bottom line but also the environment in the long term.

The right air compressor size

Selecting the correct size for your rotary screw compressor is crucial. It's essential to consider the required flow of compressed air as the primary factor in sizing. An undersized compressor won't meet your air demands, while an oversized one wastes energy. Atlas Copco's offers a variety of sizes to suit different needs, ensuring efficient operation and energy savings.  

Let's take a look at the G 2-7 range, the smallest type of compressor at Atlas Copco. Compared to piston air compressors, which are traditionally used by operations with a limited compressed air demand, they offer many advantages. They are more efficient, which reduces your costs and environmental footprint. Besides, they can run around the clock so they can handle an increased demand better. Finally, fixed-speed rotary screw compressor lower the oil content in your compressed air system, a feature that a reciprocating compressor may struggle to match.

Ready to choose your rotary screw air compressor?

Atlas Copco provides a comprehensive range of rotary screw air compressors, including the VSD, VSD+, VSDs, G, GA, and GA+ series. Each series caters to different requirements, from basic needs to demanding industrial environments, ensuring there's an Atlas Copco compressor that's right for your business.

Atlas Copco revolutionized the industry four decades ago with variable speed drive (VSD) technology, adjusting motor speed according to compressed air demand, significantly reducing energy consumption and costs. Now in their third generation (GA VSD?), they have raised the bar in every metric. This includes efficiency and sustainability, reliability, connectivity and ease of operation.

• G VSD: Our G oil-injected rotary screw compressors are designed for reliability and efficiency. Will operate continuously in the harshest environments, avoiding costly downtime and production delays.
• GA VSD+: Our market-leading GA oil-injected rotary screw compressor delivers outstanding performance, high productivity and low cost of ownership – even in the harshest environments.
• GA VSDs: When you need the best, choose VSDs. With energy savings of 60% on average compared to fixed-speed models, the GA 5-37 VSDs is the most energy-efficient compressor on the market. It also raises the bar in performance, reliability and connectivity to support your sustainability and productivity goals – now and in the future.
• GA FLX:  For those hesitant to adopt VSD technology, Atlas Copco has introduced dual-speed compressors, offering a balance between cost and energy savings. The GA FLX series combines the affordability of fixed-speed compressors with the energy savings of VSD technology, featuring two speeds to adapt to changing demand, offering up to 20% energy savings.