Centrifugal Air Compressors: How Do They Work?

Centrifugal air compressors are one example of dynamic style air compressors. The dynamic type of compressors have a continuous flow of air that has its velocity increased in an impeller that is rotating at a higher speed. The kinetic energy of the air is increased due to the increase in velocity and then becomes transformed into pressure energy through the use of a volute chamber, or a diffuser. The volute chamber is a curved funnel that increases in surface are as it approaches the discharge port. This converts the kinetic energy into pressure by allowing the velocity to reduce while the pressure increases. Approximately 1/2 of the energy is developed in the impeller and the other half is developed in the volute chamber or diffuser.

1 – Basic Centrifugal Air Compressor

The most common centrifugal air comppressor has between two and four stages in order to generate pressures up to 150 psig. A water cooled inter-cooler and separator is placed between each stage in order to remove condensation and cool the air down prior to being passed on to the next stage. These compressors still have advantages and some disadvantages. The list below showcases just a few.


  • Lubricant-free air is generated
  • Complete packages up to 1,500 hp
  • Initial costs decrease with increase in compressor size
  • No special foundations or reinforcements needed


  • Specialized maintenance requirements
  • Higher initial investment
  • Unloading/waste of air required to drop system pressures

To determine which type of compressor may be best suited for your facility, we suggest to locate and contact a compressor sales company in your geographic area. When it comes to determining the volume of air required to operate the EXAIR products and even some other point of use compressed air applications, EXAIR’s Application Engineers can help you determine the volume you will need to ensure the compressor is sized appropriately. If you would like to discuss any other point of use application, please contact us.

Brian Farno
Application Engineer

1 – Dugan, Tim PE – Basic Centrifugal Air Compressor, Compressed Air Best Practices; retrieved from https://www.airbestpractices.com/technology/air-compressors/centrifugal-air-compressor-controls-and-sizing-basics

Centrifugal Air Compressors: What are they?

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, controls 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. For the purposes of this blog, I’m going to highlight the most common style of dynamic compressor: the centrifugal air compressor.

Dynamic compressors are composed of two main categories: axial and centrifugal. These types of compressors raise the pressure of air or gas by imparting velocity energy and converting it to pressure energy. In a centrifugal air compressor, air continuously flows and is accelerated by an impeller. This impeller can rotate at speeds that exceed 50,000 rpm. Centrifugal air compressors are generally much larger and can accommodate flow ranges of 500-100,000 CFM, although they’re more commonly used in the range of 1,000 CFM to 5,000 CFM.

Centrifugal Pic 1

In a centrifugal compressor, kinetic energy is transformed into pressure energy inside of the diffuser. The air passes through the inlet guide vanes and is drawn into the center of a rotating impeller. The impeller has radial blades that push outward from the center due to centrifugal force. This radial movement of air causes an increase in pressure and the generation of kinetic energy. This kinetic energy is then also converted into pressure as it passes through the diffuser.

According to the Compressed Air Challenge, some advantages of the centrifugal air compressor include:

  • Completely packaged for plant or instrument air up through 1,000 HP
  • Relative first cost improves as the size increases
  • Designed to deliver lubricant-free air
  • Do not require special foundations
  • Ability to deliver large volumes of air (up to 100,000 CFM)

Some disadvantages include:

  • Limited capacity control
  • Poor part-load efficiency
  • High rotational speeds require special bearings, sophisticated monitoring of vibrations and clearances resulting in specialized maintenance considerations
  • High initial purchase cost

A centrifugal air compressor is just one of the many different styles utilized in industry to supply a variety of point of use compressed air products. If you have an application in your facility that could benefit from an engineered solution, give us a call. An Application Engineer would be happy to discuss your options with you and see to it that you’re getting the most out of your compressed air!

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


Image courtesy of the Compressed Air Challenge


A Brief History of Compressed Air

So where exactly did compressed air come from? How did it become so widely used and where will it go? Both of these are great questions and the answers lie below.

Compressed air can be traced all the way back to the classic bellows that were used to fuel blacksmith fires and forges.  These started as hand pumped bellows, they then scaled up to foot pumped, multiple person pumped, oxen or horse driven and then eventually waterwheel driven.  All of these methods came about due to the demand for more and more compressed air. These bellows did not generate near the amount of air pressure or volume needed for modern day practices yet they worked in the times.  These early bellows pumps would even supply miners with air.

With the evolution of metallurgy and industry these bellows were replaced by wheel driven fans, then steam came about and began generating more industrial sources of power.  The main issue with steam was that it would lose its power over longer runs of pipe due to condensing in the pipes.  Thus the birth of the air compressor was born. One of the largest projects that is noted to first use compressed air was in 1861 during the build of the Mont Cenis Tunnel in Switzerland in which they used compressed air machinery.  From here the constant need and evolution for on-demand compressed air expanded.  The picture below showcases two air compressors from 1896.

Air Compressors from the old days.

The compressors evolved over time from single stage, to two-stage reciprocating, on to compound, rotary-screw compressors, rotary vane, scroll, turbo, and centrifugal compressors with variable frequency drives.  The efficiency of each evolution has continued to increase.  More output for the same amount of input.  Now we see a two-stage compressor, considered old technology, and wonder how the company can get any work done.

All of the technological advances in compressor technology were driven by the demand sides of the compressed air systems.  Companies needed to power more, go further, get more from less, ultimately increase production.  With this constant increase in demand, the supply of compressed air increased and more efficient products for using compressed air began to evolve so the air was used more efficiently.

Enter EXAIR, we evolved the blowoff to meet the increasing demands of industrial companies to get the same amount of work done with less compressed air. We have continually evolved our product offering since 1983.  It all started with just a few typed pages of part numbers and has evolved to a 208 page catalog offering of Intelligent Compressed Air Products® for industry.  We will also continue to evolve our product designs for continued improvement of compressed air usage.  This is all to better help companies retain their resources.

EXAIR Catalog 32

If your company uses compressed air and you aren’t sure if it is efficiently being utilized, contact an Application Engineer.  Thanks for joining us for the brief history lesson, we look forward to hearing from you and seeing what the future brings.

Brian Farno
Application Engineer
@EXAIR_BF BrianFarno@EXAIR.com


Compressed air (1896) (14594022618).jpg – Wikimedia Commons – Internet Archive Book Images – Link


Supply Side Review: Heat of Compression-Type Dryers

The supply side of a compressed air system has many critical parts that factor in to how well the system operates and how easily it can be maintained.   Dryers for the compressed air play a key role within the supply side are available in many form factors and fitments.  Today we will discuss heat of compression-type dryers.

Heat of compression-type dryer- Twin Tower Version

Heat of compression-type dryers are a regenerative desiccant dryer that take the heat from the act of compression to regenerate the desiccant.  By using this cycle they are grouped as a heat reactivated dryer rather than membrane technology, deliquescent type, or refrigerant type dryers.   They are also manufactured into two separate types.

The single vessel-type heat of compression-type dryer offers a no cycling action in order to provide continuous drying of throughput air.  The drying process is performed within a single pressure vessel with a rotating desiccant drum.  The vessel is divided into two air streams, one is a portion of air taken straight off the hot air exhaust from the air compressor which is used to provide the heat to dry the desiccant. The second air stream is the remainder of the air compressor output after it has been processed through the after-cooler. This same air stream passes through the drying section within the rotating desiccant drum where the air is then dried.  The hot air stream that was used for regeneration passes through a cooler just before it gets reintroduced to the main air stream all before entering the desiccant bed.  The air exits from the desiccant bed and is passed on to the next point in the supply side before distribution to the demand side of the system.

The  twin tower heat of compression-type dryer operates on the same theory and has a slightly different process.  This system divides the air process into two separate towers.  There is a saturated tower (vessel) that holds all of the desiccant.  This desiccant is regenerated by all of the hot air leaving the compressor discharge.  The total flow of compressed air then flows through an after-cooler before entering the second tower (vessel) which dries the air and then passes the air flow to the next stage within the supply side to then be distributed to the demand side of the system.

The heat of compression-type dryers do require a large amount of heat and escalated temperatures in order to successfully perform the regeneration of the desiccant.  Due to this they are mainly observed being used on systems which are based on a lubricant-free rotary screw compressor or a centrifugal compressor.

No matter the type of dryer your system has in place, EXAIR still recommends to place a redundant point of use filter on the demand side of the system.  This helps to reduce contamination from piping, collection during dryer down time, and acts as a fail safe to protect your process.  If you would like to discuss supply side or demand side factors of your compressed air system please contact us.

Brian Farno
Application Engineer


Heat of compression image: Compressed Air Challenge: Drive down your energy costs with heat of compression recovery: https://www.plantservices.com/articles/2013/03-heat-of-compression-recovery/