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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:

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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

Fixed Speed below 50HP Variable Speed Drive below 50HP
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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

Fixed Speed above 50HP Variable Speed Drive above 50HP
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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

ALUP Oil-Free Series - Screw Air Compressor spiralAIR Scroll Compressors wisAIR Oil-Free Screw Compressors


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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

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