Tag: rotary compressor

Air Compressors: Rotary Scroll type

Published on by johnball2014Leave a comment

My colleague, Eric Kuhnash, wrote a blog “About Rotary Screw Air Compressors”, and I wanted to expand that conversation to a close cousin; Rotary Scroll type Air Compressors.  As you see in the chart below, this type of compressor falls within the same family as positive displacement compressors.

Positive displacement air compressors raise air pressure by reducing the volume of air within a confined space.  The scroll compressors use two intermeshing scrolls, where one scroll is moving and the other scroll is stationary (reference photo below).  Ambient air will get trapped at the inlet side, and as the orbiting scroll moves, the spiral volume gets smaller and smaller.  When volume decreases, the pressure will increase.  The Rotary Scroll type of air compressors is less common in the rotary family, as they are limited in capacity.    

What they lose in capacity, they make up for in simplicity.  They are compact and can fit into small areas.  They require very little maintenance; and the majority of them are oil-free.  They were initially used in refrigeration systems because they were compact, inexpensive, and required little maintenance.  Since they are quiet and oil-free, they work great in doctor’s offices and medical fields. 

No matter the type of air compressor that you use, they are very costly to operate.  To help you use them efficiently and safely, EXAIR offers a range of products that can clean, cool, blow, conserve, and convey.  This would include our Super Air Knives, Super Air Nozzles, Safety Air Guns, Cabinet Coolers, and much more.  If you want to save energy, increase safety, and cut costs no matter what size air compressor you have; you can contact an Application Engineer at EXAIR.  We will be happy to help. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Image Courtesy of the Compressed Air Challenge

Rotary Scroll GIF:  used from  Public Domain

Intelligent Compressed Air: What You Need To Know About Rotary Scroll Compressors

Published on by Russ BowmanLeave a comment

Humans have been using compressed air for just about as long as we’ve been using fire. The discovery of fire’s usefulness likely only slightly predates the discovery that blowing air on those flames increases their size, temperature, and intensity. Technically, our respiratory systems are single-stage, diaphragm operated air compressors!

Over the ages, engineer-type humans came up with mechanical methods to perform this task, which was primarily used to stoke fires. This was critical to the development of metalworking, which was key to the Industrial Revolution, which brought on more needs for compressed air, which led to better-equipped engineer-type humans developing the modern methods by which we compress air.

One of the most recent inventions to do this is the rotary scroll compressor. Similar to other rotary type compressors, they use a rotating shaft to decrease the space occupied by a specific amount of gas. By decreasing the space occupied without letting any of that gas out, the pressure increases. The “tricky” part about rotary scroll compressors is the incredibly tight tolerances needed to make it function effectively. In fact, the first patent for one (issued in 1905) predates the machining technology needed to make one by about forty years. And it was the 1970’s before they started to be manufactured for commercial use. Here’s how they work:

Two spirals, or scrolls, are intermeshed. The rotating (black) one orbits eccentrically with the fixed one, continually decreasing the volume for the gas to flow through (from the outer left & right sides) as it is pushed to the center, where it is fully compressed according to the compressor’s rating.

Key advantages/benefits of this design are:

  • Oil free air – no metal to metal contact of the scrolls means no lubrication is needed in the airend.
  • Pulsation free delivery – since the flow from suction to discharge is one continuous motion, the outlet pressure is constant and even.
  • Quiet operation – the lack of metal to metal contact, and continuous motion eliminate the mechanical noise inherent in, for example, the reciprocating pistons and slamming check valves in a piston type compressor.
  • Low maintenance – as in most cases, less moving parts = less to maintain.
  • Wide range of duty cycle – their design makes them particularly conducive to single & two-stage units, and efficient operation with modulating variable speed drives, meaning they handle low loads just as effectively as high loads.

Some disadvantages/drawbacks are:

  • Higher price tag – the precision machine tools, and their skilled operators, are not cheap, and neither are rotary scroll compressors.
  • Size restrictions – larger rotating scrolls generate higher centrifugal force. Because the tolerances are so tight, those higher forces necessarily limit the mass of the rotary element, which limits the size, and hence, the air flow they can push out. As a result, they’re limited to the neighborhood of 100 SCFM capacity.

This combination of pros & cons makes rotary scroll compressors especially popular in the medical and laboratory settings. A supply of clean air at a constant pressure, with the ability to handle constantly changing loads matter a LOT in those settings. 100 SCFM is a LOT of air flow in most of their applications, and relatively speaking, the air compressor generally isn’t even close to the highest priced piece of equipment in such facilities.

At EXAIR Corporation, we’re committed to help you get the most out of your compressed air system. To do that, it’s important to have a better understanding of these systems, from generation to end use. If you’d like to find out more, give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
Visit us on the Web
Follow me on Twitter
Like us on Facebook

Rotary Scroll GIF:  used from  Public Domain
Images Courtesy of  Compressor1 Creative Commons.

Rotary Air Compressors: How Do They Work?

Published on by Tyler DanielLeave a comment
Ingersoll Rand Rotary Screw Compressor

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, control systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy. We’ve discussed the different styles of air compressors here on the EXAIR Blog in the past. Today I’d like to highlight the rotary compressors, one of the positive-displacement types of compressors.

Positive-displacement compressors are broken into two categories: reciprocating and rotary. The rotary compressors are available in lubricant-injected or lubricant-free varieties. Both styles utilize two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point inter-meshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure.

In the lubricant-injected varieties, the compression chamber is lubricated between the inter-meshing rotors and bearings. This lubricant protects the inter-meshing rotors and associated bearings. It eliminates most of the heat caused by compression and acts as a seal between the meshing rotors and between the rotor and stator. Some advantages of the lubricant-injected rotary compressor include a compact size, relatively low initial cost, vibration free operation, and simple routine maintenance (replacing lubricant and filter changes). Some drawbacks to this style of compressor include lower efficiency when compared with water-cooled reciprocating compressors, lubricant carry over must be removed from the air supply with a coalescing filter, and varying efficiency depending on the control mode used.

In the lubricant-free varieties, the inter-meshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an inter-cooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

Each of these compressors can deliver air to your Intelligent Compressed Air Products. If you’re looking to reduce your compressed air consumption and increase the safety of your processes contact an EXAIR Application Engineer today. We’ll be happy to discuss the options with you and make sure you’re getting the most out of your compressed air usage.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD




Photo courtesy of Ingersoll Rand CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=32093890

Intelligent Compressed Air: Rotary Air Compressors

Published on by Tyler DanielLeave a comment

Air Compressor
Air Compressor and Storage Tanks

One thing that is found in virtually every industrial environment is an air compressor. Some uses for the compressed air generated are: powering pneumatic tools, packaging, automation equipment, conveyors, control systems, and various others. Pneumatic tools are favored because they tend to be smaller and more lightweight than electric tools, offer infinitely variable speed and torque, and can be safer than the hazards associated with electrical devices. In order to power these devices, compressed air must be generated.

There are two main categories of air compressors: positive-displacement and dynamic. In a positive-displacement type, a given quantity of air is trapped in a compression chamber. The volume of which it occupies is mechanically reduced (squished), causing a corresponding rise in pressure. In a dynamic compressor, velocity energy is imparted to continuously flowing air by a means of impellers rotating at a very high speed. The velocity energy is then converted into pressure energy. We’ve discussed the different styles of air compressors here on the EXAIR Blog in the past. Today I’d like to highlight the rotary compressors, one of the positive-displacement types of compressors.

Positive-displacement compressors are broken into two categories: reciprocating and rotary. The rotary compressors are available in lubricant-injected or lubricant-free varieties. Both styles utilize two inter-meshing rotors that have an inlet port at one end and a discharge port at the other. Air flows through the inlet port and is trapped between the lobes and the stator. As the rotation continues, the point inter-meshing begins to move along the length of the rotors. This reduces the space that is occupied by the air, resulting in an increase in pressure.

In the lubricant-injected varieties, the compression chamber is lubricated between the inter-meshing rotors and bearings. This lubricant protects the inter-meshing rotors and associated bearings. It eliminates most of the heat caused by compression and acts as a seal between the meshing rotors and between the rotor and stator. Some advantages of the lubricant-injected rotary compressor include a compact size, relatively low initial cost, vibration free operation, and simple routine maintenance (replacing lubricant and filter changes). Some drawbacks to this style of compressor include lower efficiency when compared with water-cooled reciprocating compressors, lubricant carry over must be removed from the air supply with a coalescing filter, and varying efficiency depending on the control mode used.

In the lubricant-free varieties, the inter-meshing rotors have very tight tolerances and are not allowed to touch. Since there is no fluid to remove the heat of compression, they typically have two stages of compression with an inter-cooler between and an after cooler after the second stage. Lubricant-free compressors are beneficial as they supply clean, oil-free compressed air. They are, however, more expensive and less efficient to operate than the lubricant-injected variety.

Each of these compressors can deliver air to your Intelligent Compressed Air Products. If you’re looking to reduce your compressed air consumption and increase the safety of your processes contact an EXAIR Application Engineer today. We’ll be happy to discuss the options with you and make sure you’re getting the most out of your compressed air usage.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD