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Centrifugal Air Compressors Explained – All You Need to Know

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A centrifugal flow compressor is a form of dynamic compressor that contains a radial design. This radial design operates at a constant pressure rather than a constant volume flow like displacement compressors.

This page will provide you with all the relevant information on centrifugal air compressors to help you better understand them, including how they work, their performance vs other types of compressors, and common applications.

Table of Contents

What Is a Centrifugal Air Compressor?

Centrifugal Air Compressors are a form of dynamic compressor, that efficiently convert the kinetic energy of a rotating compressor fan into compressed air utilizing a series of stages to compress and cool the air as it continuously flows through the compressor.

Centrifugal air compressors are reliable, efficient, and compact devices that allow for the management of air compressor capacity at constant pressures due to their modern software controls.

They typically use gears but some modern configurations of the centrifugal air compressor have started to adopt very high-speed electric motors to drive the impellers. These configurations are suited to applications that require oil-free air as they operate without a gearbox and its accompanying oil-lubrication needs.

Their performance can be affected by numerous external conditions that may be difficult to control like the change in inlet temperature.

How Does a Centrifugal Compressor Work?

Centrifugal compressors draw air into the center of their rotating impeller using their radial blades. The flow in the centrifugal air compressor radially recedes from the driving shaft perpendicular to its motion. This air is then pushed towards the center due to the centrifugal force present.

The radial movement of air increases the kinetic energy which can be converted into pressure (a form of potential energy) thanks to a diffuser and volute. You could say that the kinetic energy itself causes pressure rise, but the process is not that simple.

A diffuser is a stationary component that acts as a radial passage near about the same width as the impeller blades. This primarily works to convert the velocity energy of the air (kinematic energy) into pressure (potential/static energy). The radial area of the diffuser expands and this expansion causes the desired diffusing effect to occur.

The blades essentially produce a higher pressure variation very similar to an airfoil of a spinning propeller on an aircraft or wind turbine. The key difference is that the blades are far closer together on a centrifugal air compressor. This closeness of the blades and the complexity of the design causes a serious alteration in flow between the blades which can be very unsteady.

The centrifugal compressors are built in stages, and each stage has a part to play in the overall discharge pressure increase of the system. The stages can vary depending on the application of the course.

In modern-day centrifugal air compressor designs you will find ultra-high-speed electric motors being used to drive the impellers. These electric motors provide a compact compressor without a gearbox and associated oil-lubrication system, therefore making them oil-free and suitable for applications that require 100 percent oil-free air.

Centrifugal Air Compressor Design

A centrifugal flow compressor is designed to thrive in conditions that have higher capacities due to the continuous airflow through their multiple stages. In most cases, typical centrifugal air compressors have three stages within industrial plants. This is because air systems within plants need on average about an 8:1 pressure increase and centrifugal compressors offer about 2:1 or 3:1 per stage.

Between each stage in the compressor, intercoolers are found and at the exit of the final stage (in this case, the third stage) an after-cooler can be found. The intercoolers cool the compressed air coming out of each of the drive air compression stages and remove excess moisture before the air passes into the next stage.

This can have a positive impact on the compressed air quality and resulting efficiency of the system. The compressor is mounted on a base that contains:

  • Driver – typically a motor
  • Gears – bull gear with pinion gear – these drive the air compressor stages
  • Stages – amount vary depending on the application
  • Coolers – intercoolers and after-cooler
  • Piping – connecting the system
  • Valves – inlet guide vanes, blow-off valve, check valve
  • Modern controls – in most cases, a control panel

Performance Comparison vs. Other Compressor Types

Axial Compressor vs Centrifugal Compressor

As centrifugal flow compressors are a type of dynamic compressor, it is only right to compare them against the other form of a dynamic compressors. Now, introducing axial flow compressors.

Axial flow compressors have a far more complex design than centrifugal compressors which results in more difficult manufacturing operations, more components, higher price per unit, and significantly higher maintenance costs.

As you have learned from this article, the flow in the centrifugal air compressor radially recedes from the driving shaft perpendicular to its motion. On the other hand, the axial compressor’s flow direction is parallel to the axis of its shaft.

Axial compressors are far more suited to designs with multi-stages and have smaller frontal areas. Centrifugal compressors can boast difficulties if a multi-stage requirement is desired.

In regards to the ever-so-important pressure ratio. The centrifugal air compressor achieves the highest per-stage ratio in comparison to the axial which develops a very low-pressure ratio per stage. This leads to the requirement for more stages, which may become a hassle or difficulty.

Centrifugal Compressors vs Positive Displacement Compressors

The positive displacement compressors have a very high-pressure ratio when compared to these two dynamic compressors.

Axial compressors hold the best efficiency rating, higher than centrifugal and positive displacement compressors. This is primarily at large capacities because positive displacement compressors are generally the best for small capacities.

Specifically looking at a centrifugal vs reciprocating air compressor, which is a type of positive displacement compressor. It can be said that a centrifugal air compressor typically has better isothermal efficiency and isentropic efficiency. Importantly, they require far less maintenance than reciprocating compressors.

However, if the pressure ratio is greater than two, it is likely that the reciprocating compressors will operate with far better efficiencies. And although they require more maintenance, they’re a lot easier and cheaper to repair.

Reciprocating compressors require more maintenance than centrifugal compressors due to their multistage operation. Though this may be worth it for a wide array of applications as it is certainly advantageous. Reciprocating compressors are far more flexible and work significantly better with varying pressures.

Centrifugal Air Compressor Applications

  • Pipeline booster services
  • Onshore and offshore gas lift services
  • Chemical plants
  • Gas injection
  • Transmission and storage of natural gas
  • Jet engines
  • Turbojets
  • Turboshafts

A centrifugal air compressor is best suited for applications above 200 horsepower for the reasons stated previously. They have numerous applications across a variety of industries with the most notable being process gas compression applications and those listed above.

The centrifugal air compressor is more widely used in industrial applications and for this reason, it is also known as a petroleum and chemical air compressor for the industry. Due to its modern aerodynamic technique, accurate rotating parts, modern control mode, and variable-speed technologies, the centrifugal air compressor has become far more popular for use in chemical industries.

How Reliable Is a Centrifugal Air Compressor?

Centrifugal air pumps and compressors, like any other type of air compressor, certainly undergo faults and may require maintenance and servicing of high quality at times.

They have very complex designs and therefore require great testing to determine their performance before manufacturing. Wind tunnels and advanced computational models are used to determine the design’s performance and therefore can result in more reliable gas compressors.

They offer high-volume capabilities in relatively compact scenarios and can be extremely reliable compressors when applied properly. This can be said for any of the varying dynamic compressors.

Reliability of a centrifugal air compressor will inevitably be a function of how well it is maintained. Seek guidance and support from the OEM and ensure you follow a rigorous preventative maintenance regime for your centrifugal air compressor to maximise it’s performance, efficiency and life expectancy.

Centrifugal Air Compressor Manufacturers & Where to Buy

Though I couldn’t find any centrifugal air compressors direct on Amazon, your best bet is to visit the manufacturer’s websites directly.

For example, Ingersoll Rand offers a variety of centrifugal air compressors and you can browse their catalog here. Other notable centrifugal air compressor manufacturers include:

FAQs (Frequently Asked Questions)

What is a centrifugal air compressor?

Centrifugal air compressors are a type of dynamic compressor that are reliable, efficient, and compact devices that allow for the management of air compressor capacity at constant pressures due to their modern-like controls. They efficiently convert the energy utilizing a series of stages to compress and cool the air as it continuously flows through the compressor.

What is the purpose of centrifugal air compressor?

The purpose of a centrifugal air compressor is to compress large volumes of air to constant pressure. They increase the kinetic energy of the gas with a high-speed impeller and then convert this energy into increased pressure in a divergent outlet passage known as the diffuser.

What is the advantage of centrifugal compressor?

An advantage the centrifugal air compressor holds over axial flow compressors, the other type of dynamic compressor, is that they are far easier to design and manufacture. They can typically increase the pressure enough with only one stage, while axial compressors may require multi-stages.

How is air compressed in a centrifugal compressor?

Centrifugal compressors compress air by first drawing it into the center of their rotating impeller using their radial blades. Centrifugal forces then push this air towards the center. The radial movement of air increases the kinetic energy which can be converted into pressure (a form of potential energy) thanks to a diffuser and volute.

Other Types of Air Compressors

If you’re interested in finding out more information on other types of air compressors please visit our specific pages:

If you have any questions regarding centrifugal air compressors, please leave a comment below with any photos if applicable so that someone may help you!

By Aidan Weeks

A passionate Mechanical Engineer with endless enthusiasm for fluid power - building off the back of over 18 years of high quality contribution and discussion stimulated by Bill Wade here at About Air Compressors. With both practical and theoretical experience in pneumatics and hydraulics, I'm putting my knowledge to work - and working my grey-matter through my research, assistance and publishing work here at About Air Compressors. Feel free to reach out any time! P.S. A HUGE shout out to Doug who really offers such great value to all visitors to About Air Compressors - once again, feeling like I'm standing on the shoulders of GIANTS by getting to work alongside such a great community

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