How to pick the right rotary screw compressor

When an industrial application calls for a steady supply of quality air, more and more users are turning to rotary screw compressors. Their efficiency, reliability and versatility make them a great choice in these cases. But there are countless applications and many different types of rotary screw air compressors. So which one is the right one for you?

First, let’s look at 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 around the clock - 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.

Fixed-speed and variable speed rotary screw compressors

The first major distinction is the one between fixed-speed and variable speed rotary screw air compressors. As the name indicates, the former run at a single speed. That makes them a great choice for applications with a steady air demand (and the more steady that demand, the more efficient they are).

Variable speed drive (VSD) compressors, on the other hand, adjust their motor speed to the amount of air that is needed. As a result, they can take their efficiency to another level if the compressed air demand fluctuates.

If that applies to you, you can learn more here about our VSD series.

This article primarily deals with the different types of fixed-speed rotary screw compressors. That means if your air demand is constant, you should read on for important information. 

Oil-free and oil-injected rotary screw compressors

Having narrowed your selection to fixed-speed compressors, the next step is to choose between oil-free or oil-injected models. 

The difference is that the latter introduces a new contaminant into the compression process. Therefore, you would pick an oil-free compressor if the presence of oil vapors matters – for example if your industry is subject to air purity standards. This includes the pharmaceutical industry, the food and beverage sector and semiconductor manufacturing.

Here, oil-free technology is a better alternative than using an oil-injected model and then filtering out the contaminant.

If air quality is less important, for example if you need the compressor to power pneumatic tools, then an oil-injected model will generally suffice.

Two drive types, lots of benefits

Atlas Copco offers its fixed-speed rotary screw compressors with two types of drives. Depending on your application, each of them has different advantages.

-Belt drive: Fixed-speed rotary screw compressors with belt drives are very robust. They are the least expensive and are easy to install, operate and maintain. For all of these reasons, they are a popular choice for smaller operations.

-Gear drive: A gear drive makes a compressor quieter. That means you can install it in more places without violating noise standards. Their initial investment cost is a little higher. However, because they are more efficient and maintenance free, rotary screw compressors with gears are less expensive to operate. This will allow you to quickly recoup that higher cost. 

Get in touch with one of our experts

Getting your compressor size right

No matter which type of compressor you choose, it is very important that you get its size right. If the unit is too small, it may not get the job done. If it is too large, you will waste a lot of valuable energy.

However, rotary screw compressors are a good deal with lots of benefits at any size.  Compared to piston air compressors, which are traditionally used by operations with a limited compressed air demand, they offer many advantages. First and foremost, they are more efficient, which reduces your costs and environmental footprint.

Because they can run around the clock, they can handle an increased demand better. Finally, fixed-speed rotary screw compressor lower the oil content in your compressed air system.

And the larger your compressor gets, the more you can save down the road. 

A complete offer

Ash Air offers a complete range of oil-injected fixed-speed compressors for different types of users with different priorities:

Below 50HP - Screw Air Compressors

Chicago Pneumatic rotary screw air compressors are built on the very robust platform and feature state of the art controller and high-efficiency screw element.

The Ash Air range of oil lubricated screw air compressors are excellent all-in-one solutions for small and medium workshops, with energy cost savings of 30% - 35%. The most popular air compressors 10HP, 15HP, and 20HP are available as a full feature with integrated air dryer and receiver. More than 100 rotary air compressors available for sale from stock in Auckland and Christchurch.

Direct driven air compressors with variable speed drives offer high energy efficiency, a smooth start and prolonged life of the component parts, reduced system pressure and energy consumption.

Sub Categories

Above 50HP - Screw Air Compressors

For power above 45 kW we offer ALUP air compressors, designed and manufactured in Europe. We installed Alup rotary screw air compressors at dozens of sites in New Zealand for food processing, at timber plants and other industrial sites.

These high-efficiency rotary screw air compressors feature variable speed drives, remote monitoring and heat recovery options. ALUP air compressor is covered by an optional 5 years warranty.

The three most popular air compressors 45 kW, 55kW and 75 kW are available for sale from stock in Auckland. Chat to our experts, we will help you to answer questions about what can you use the compressor for, what compressor is the best and learn all about air compressor efficiency.

Sub Categories

Oil Free - Screw Air Compressors

The team at AshAir specialises in oil-free or oil-less scroll compressors with zero risk of oil contamination, and are ideal for critical applications including medical, pharmaceutical, dental, R&D, food & beverage, wine and brewery. Our 100% oil-less scroll compressors are designed with fewer moving parts, which means less wear and tear, less noise, higher efficiency and reliability, and a longer machine life .

These scroll compressors use cutting-edge scroll technology where the spirals never contact each other, and no lubrication is needed, making them completely oil-free. Our SPR 20 Multi oil-less scroll compressor operates with variable air delivery, controlled by an intelligent controller for air delivery supplied according to the fluctuation of air demand. This means a higher energy efficiency and more stable system pressure.

Sub Categories


Do you have an idea for our #expertcorner? Let us know!

Who we are and how Ash Air can help your business!

Ash Air has been around in New Zealand since 1979, and we’ve grown into a nationwide company with international support and a reputation for quality and reliability.We look after all things compressed air for your business!

  • Rotary Screw and Piston Air Compressors
  • Vacuum Pumps and Blowers
  • Nitrogen Generation
  • An extensive line of Air Treatment components
  • AIRnet Piping System and  Filtration
  • Mobile Compressors, Generators, and Light Towers

Ash Air's range of Chicago Pneumatic, ALUP, Pneumatech, and Atlas Copco products are used extensively around the world in industries ranging from oil and gas to food, automotive and farming, and we bring you these world-class compressors here in the land of the long white cloud.Our technicians are compressed air equipment experts and are dedicated to addressing customer needs. Supported with nationwide coverage, Ash Air offers one of the widest selections of compressed air, vacuum pump, and industrial gas equipment and parts available today in New Zealand.

Reliability and Efficiency

With Ash Air, you can count on reliability and high performance for even the most demanding applications. We focus our efforts on the following:

  • Increasing uptime
  • Reducing unexpected repairs
  • Reducing energy consumption and meeting our sustainability goals
  • Improving the cleanliness of compressed air


Talk to the team today:  CONTACT US CONTACT US

Read more from our #expertcorner


Air compressor leaks can be a substantial source of wasted energy in any system, sometimes wasting 20-30% of a compressor's production. Worst of all, a poorly maintained compressor can have a leak rate expected to equal 20% of total compressed air...


Choosing the right compressor is essential to your long-term satisfaction and maybe, to the profitability of your business. Many times compressors are based on a single factor alone, such as horsepower or tank size, which is only part of the story.


In oil injected screw compressors, there is a thin layer of oil found between the rotors to create a seal and maintain proper efficiency as the compression occurs. The unfortunate side effect of this solution is that oil may carry over to the point of use in your air system. This can be mitigated by having correct filtration in place to remove the oil contaminants in your air. Additionally, many individuals may decide to opt for a completely oil-free solution, with the use of a scroll compressor or water injected screw compressor.


Most businesses concentrate on the air compressor and consider the piping as a secondary concern. The piping system can make or break your business. Faulty, inefficient piping can cause pressure loss and lost power. Keeping a close eye on the overall layout, installations and maintenance of your air piping system will help keep your business running at its’ optimal efficiency.


Our #1 Focus is Customer Service! Whether you have questions about which compressor is right for you, or if you’re ready to improve your operations and start saving on expenses. Ash Air has been around for over 40 years because we offer reliable and hardworking air compressors, vacuum pumps, and services as well as expert advice and support.


An oil analysis can prevent problems later down the road. It's often been referred to as the blood test for your compressor. Just like a blood test can tell you about your health and early alerts to impending problems, an analysis can do the same for your compressor.




Did you know that pressure drops and leaks are the two largest areas of energy loss on your air compressors? It’s easy to understand why a leaking pipe or fitting creates energy loss. Pressure drops are not quite as noticeable, since you cannot hear ...


Whenever anything doesn't work properly, it's frustrating and we get it. If this is your first time experiencing troubles with your dryer, you're probably unsure where to even start. Getting your dryer repaired and back up and working is critical to ...


Screw compressors are helpful for an enormous range of applications such as air filling, packaging, tools, HVAC control, and more! One possible drawback is the amount of electricity they use; air compressors can be a huge drain on energy if used ​ine...



Most air compressors require constant oil lubrication to prevent friction on the pistons or screws and other moving parts. To make sure your air compressor is running efficiently, it is important to check your oil level regularly and to know how much...


Have you heard of the term "Total Air Solutions"? A total air solution means everything that goes with the compressor for your business’s air system. 90% of companies require more than just an air compressor. 


When speaking of air compressors, compressed air treatment is a process that dehumidifies and cleans air before entering the compressor. Most commonly, this process involves air filters and an air dryer.


Air compressors are used in many different applications and provide essential compressed air to many businesses and individuals with different air needs. No matter what your CFM, PSI and HP requirements are, the electronic controller on your air compressor is the motherboard for keeping your unit running as efficiently as possible. It is your eyes into your machine.


Air compressors are helpful for an enormous range of applications such as air filling, packaging, tools, HVAC control, and more! One possible drawback is the amount of electricity they use; air compressors can be a huge drain on energy if used ​inefficiently​. If you are running them too long, allowing leaks to exist, or using the wrong type of compressor, you are wasting ​energy and money​. This article will go over some of the biggest power-wasters and how to
stop/prevent them!



In the following guide, we want to try to answer some of the questions you may have been asking yourself in regards to screw air compressors. If you do not find the answer you are looking for, please get in touch with us.


Compressed air is a key utility supporting the food packaging and food processing industries. It is used in machines that fill products such as cakes, pies, and liquid products, as well as during the packaging and transportation of snacks, vegetables, beer, soda and other items.. Compressed air must be moisture and contaminant-free to ensure the protection of the food products processed in each facility. 


Minimizing the risk of accidents in the workplace is a top priority in industry, and it is especially important when working with pneumatic power tools. Ensuring that all safety precautions have been taken to protect the health and wellbeing of operators is vital. With this in mind, here are seven simple steps to reduce the risk of accidents and improve operator safety


Regardless of the type of compressor you have, vibration issues can be troubling for any business. The root of the vibration can stem from multiple sources, some internally and others externally. Understanding the cause of the vibration and how to resolve them will be critical in keeping your compressor in proper working order.


Air compressors are essential to your business, but they can also become a safety hazard when used improperly. Reading your owner’s manual and following all proper safety precautions before use is vital in keeping your compressor in great, working condition.


Corrosion in the pipeline is due to insufficient condensation drainage that occurs during compression. The resulting condensate, together with the compressed air, flow further into the compressed air line network and has a negative effect on the pipes. Find out more about how you can prevent corrosion here.


FRLs – Filters, Regulators and Lubricators – guarantee the efficiency and durability of pneumatic tools. Including an FRL in your air system is vital to running an efficient air line set-up and key to achieving a good return on investment. Read more here!


Check out this blog and video included to help you know what you should be looking for when you're thinking about purchasing a Chicago Pneumatic Rotary Screw Compressor for your shop or application. If you want to learn about what a screw compressor actually is, check out this article  


There are 3 simple steps to make sure your air line installation is providing the right pressure and that your accessories selection is correct, so you can ultimately work productively. It does not take long and it is something you can easily do yourself using our self-diagnostic checklist. 


Okay, okay, we're a bit excited. With the recent launch of our air tools in our online shop. Here's a 101 for you about what air tools you might need in your air compressor tool kit. Air tools are prevalent in automotive industries, woodworking, construction, metalwork and more. Did you know that there's pretty much an air-powered version nearly any power tool on the market? We want to share with you our 'Must have Air Tools'.


When you are thinking about an air compressor, you might be have the image of the super popular piston or reciprocating compressor in your mind. The compressor that you see in home workshops, automotive garages pumping up tyres and assisting in spray painting cars.


As a follow on to our Why You Should Not Use PVC Piping for Your Compressed Air System blog, we share with you what piping you shouldbe using to get the most out of your compressed air system. Here at Ash Air we have the perfect solution if you're wanting to match your great compressor with a fast, easy and reliable piping solution that supports the operational excellence of your whole compressed air system. 


An air compressor is a big purchase for any business. It is visibly important to properly maintain the air compressor and filter elements to protect that investment. Air intake filters are installed in an air compressor to remove any dust or debris the compress may suck in. Dust will cause wear to the compressor element, valves, filters, compressor oil and any moving parts.


So you have a vacuum pump installed and you rely on it for your business operations and performance? Here are some reasons why you should consider overhauling your vacuum pump! s with all machinery and compressed air equipment, regular maintenance can help ensure optimised safer performance of your vacuum pump. Learn more about benefits of restoring, rebuilding and repairing your vacuum pump.


Air compressors are used every day, by many industries around the world. They are often considered the heart of a business, in that most companies will rely on their performance and efficiency to run their operations, to get work done effectively and safely. In your day to day, you've probably seen air compressors in use - whether at a build site powering construction equipment or in a mechanics workshop inflating tyres.


A scroll air compressor, or spiral compressor, compresses air by drawing it it, trapping it, reducing the volume and discharging it at the outlet port. The scroll compressor that you see today, such as SpiralAIR, have been the result of modernised advancements in manufacturing technology, even thought the concept of a scroll compressor has been around for over 100 years.The scroll compressor is oil-free orbiting, or positive displacement compressor. The compressor has a stator spiral fixed in a housing, and a motor driven eccentric orbiting spiral.Â