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

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

Rotary Scroll Compressors

Over the years, my EXAIR colleagues and I have blogged about different types of air compressor types including single and double acting reciprocating, rotary screw and sliding vane air compressors. You can click on the links above to check those out. Today, I will review the basics of the rotary scroll-type compressor.

The rotary scroll type compressor falls under the positive displacement-type, the same as the other types previously discussed.  A positive displacement type operates under the premise that a given quantity of air is taken in, trapped in a compression chamber and the physical space of the chamber is mechanically reduced.  When a given amount of air occupies a smaller volume, the pressure of the air increases.

Positive displacement type compressors

Each of the previous positive displacement type compressors use a different mechanism for the reduction in size of the compression chamber. The rotary scroll uses two inter-meshing scrolls, that are spiral in shape. One of the scrolls is fixed, and does not move (red).  The other scroll (black) has an “orbit” type of motion, relative to the fixed scroll. Air would be drawn in from the left, and as it flows clockwise through the scroll, the area is reduced until the air is discharged at a high pressure at the center.

How it Works

There is no metal to metal sliding contact, so lubrication is not needed.  A drawback to an oil free operation is that oil lubrication tends to reduce the heat of compression and without it, the efficiency of scroll compressors is less than that of lubricated types.

The advantages of the rotary scroll type compressor include:

  • Comes as a complete package
  • Comparatively efficient operation
  • Can be lubricant-free
  • Quiet operation
  • Air cooled

The main disadvantage:

  • A limited range of capacities is available, with low output flows

EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.

If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Jordan Shouse
Application Engineer

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

 

About Rotary Scroll Compressors

The Rotary Scroll compressor is a popular style compressor and is used primarily for air conditioning refrigerant systems.  Recently, since it is very efficient, quiet and reliable it has been adopted by industrial air compressor manufacturer’s to expand their product offering for their smaller, high-efficiency product line.

They operate on the principle of two intermeshing spirals or scrolls with one being stationary while the other rotates or orbits in relation to it.  They are mounted with 180° phase displacement between them which forms air pockets having different volumes.  Air enters through the inlet port located in the rotating/orbiting scroll which fills the chambers and as is moved along and compressed along the scroll surfaces.

Some of the key advantages of a Rotary Scroll Compressor are:

  • Pulsation free delivery due to the continuous flow from the suction port to the outlet port.
  • No metal to metal contact thereby eliminating the need for lubrication
  • Low noise levels
  • Fewer moving parts means less maintenance
  • Energy Efficient
  • Air cooled

The largest disadvantage is they are available in a limited range of sizes and the largest SCFM outputs are around 100 SCFM.

This is exactly where EXAIR shines, we offer 15 product lines of highly efficient & quiet point of use compressed air products and accessories to compliment their limited output volume of air.  All EXAIR products are designed to use compressed air efficiently and quietly, many of which reduce the demand on your air compressor which will help control utility costs and possibly delay the need to add additional compressed air capacity.

As an example, EXAIR’s Super Air Knives deliver exceptional efficiency by entraining ambient air at ratios of up to 40:1 and they are able to deliver an even laminar flow of air ranging from a gentle breeze to exceptionally hard-hitting force.

Super Air Knife
EXAIR’s Super Air Knife entrains ambient air at a 40:1 ratio!

EXAIR’s Super Air Amplifiers are able to entrain ambient air at ratio’s up to 25:1.  The model 120024 – 4″ Super Air Amplifier developes output volumes up to 2,190 SCFM while consuming only 29.2 SCFM of compressed air @ 80 PSI which can easily be operated on a 100 SCFM output compressor.

Super Air Amplifier
EXAIR Air Amplifiers use a small amount of compressed air to create a tremendous amount of air flow.

For your blow off needs EXAIR’s Super Air Nozzle lineup has an offering that will fit nearly any need or application you may have.  Nozzles are available in sizes from M4 x 0.5 to  1 1/4 NPT and forces that range from 2 ounces of force up to 23 Lbs at 12″ from the discharge.  We offer sixty two nozzles that could all be operated easily from the limited discharge or a rotary scroll compressor.

nozzlescascadeosha
Family of Nozzles

If you need to reduce your compressed air consumption or you are looking for expert advice on safe, quiet and efficient point of use compressed air products give us a call.  We would enjoy hearing from you!

Steve Harrison
Application Engineer
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Rotary Scroll-Type Compressor

Over the last few months, my EXAIR colleagues and I have blogged about several different types of air compressor types including single and double acting reciprocating, rotary screw and sliding vane air compressors. You can click on the links above to check those out. Today, I will review the basics of the rotary scroll-type compressor.

The rotary scroll type compressor falls under the positive displacement-type, the same as the other types previously discussed.  A positive displacement type operates under the premise that a given quantity of air is taken in, trapped in a compression chamber and the physical space of the chamber is mechanically reduced.  When a given amount of air occupies a smaller volume, the pressure of the air increases.

Each of the previous positive displacement type compressors use a different mechanism for the reduction in size of the compression chamber. The rotary scroll uses two inter-meshing scrolls, that are spiral in shape. One of the scrolls is fixed, and does not move (in red).  The other scroll (in black) has an “orbit” type of motion, relative to the fixed scroll. In the below simulation, air would be drawn in from the left, and as it flows clockwise through the scroll, the area is reduced until the air is discharged at a high pressure at the center.

Two_moving_spirals_scroll_pump
How it Works- A fixed scroll (red), and an ‘orbiting’ scroll (black) work to compress the air

It is of note that the flow from start to finish is continuous, providing air delivery that is steady in pressure and flow, with little or no pulsation.

There is no metal to metal sliding contact, so lubrication is not needed.  A drawback to an oil free operation is that oil lubrication tends to reduce the heat of compression and without it, the efficiency of scroll compressors is less than that of lubricated types.

The advantages of the rotary scroll type compressor include:

  • Comes as a complete package
  • Comparatively efficient operation
  • Can be lubricant-free
  • Quiet operation
  • Air cooled

The main disadvantage:

  • A limited range of capacities is available, with low output flows

EXAIR recommends consulting with a reputable air compressor dealer in your area, to fully review all of the parameters associated with the selection and installation of a compressed air system.

If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

Rotary Scroll GIF:  used from of Public Domain