An air compressor (compressed air to power work tool) is an essential tool in any workshop with a wide range of applications. They are used for a variety of applications, such as running different air-powered tools. This machine is an essential part of a lot of our lives, and it most probably is or will be valid for you too, since you are here reading this article. Chances are you are going to buy a compressor and doing your research before choosing an appropriate air compressor according to your need. But this is not an easy task.

There are various types of air compressors, and these categorizations are done in multiple ways. They are classified based on tank size, CFM (cubic feet per minute) output, horsepower, and many other things. These categories are created to use in different operations and to complement specific requirements of any particular function. For instance, reciprocating vs. rotary, fixed speed vs. variable speed? Oil-flooded vs. oil-free, and many others. So, you have to know the different air compressor types and think carefully before choosing the air compressor technology that best matches your needs and works and improves overall operation.

Different type of air compressors

There are two main types of air compression methods that are used in compressors. To understand the working principle of a compressor, it’s wise to first learn about the different types of compressors and the air compression method they use.

  • Positive displacement air compression
  • Dynamic displacement air compression

1. Positive displacement air compression

The working principle of the positive displacement type compression systems is to inhale the air into the compression chamber, then compress the air by reducing the volume of air through implementing pressure. After the compression is done through pressure increase, the discharge valves open to move the air to the storage tank from the compression chamber by force. Examples of positive-displacement air compressors include reciprocating, rotary-screw, piston, vane, and scroll-type air compressing systems.

⦿ Reciprocating/Piston compressor

Reciprocating compressors work by using positive displacement. They use pistons, which are controlled by the crankshaft for their downward and upward strokes. The downward strokes of the piston rod inhale the airflow into the chamber, and the upward strokes, move the compressed air stream to the air storage tank.

These types of piston technology-based compressors have a comparatively lower output, but they are able to provide a higher pressure output than others. So, these piston-based air compressors are usually found at smaller worksites and aren’t designed for continuous use.

This type of piston air compressor is suitable if you want to compress a small amount of air but implement high air compressor pressure. Also, It is able to dissipate the heat produced during the compressing process.

Teflon piston ring is usually used for non-lubricated compressors of this type. It reduces wear and eliminates the need for lubrication of pistons, rings, and cylinders.

Piston compressors are of two major types based on their stages of compression.

  • Single-stage compressor
  • Two-stage compressor

Basically, single-stage compressors use a single phase of compression to compress the air. On the other hand, dual-stage compressing machines have two compression stages and carry out another phase of compression along with the first one.

You can click here to learn more about the single-acting compressors and double-Acting Compressors, how does a single-stage or a two-stage air compressor works, and the differences between a single-stage compressor and a dual-stage compressor.

⦿ Rotary Compressor

There are five basic types of rotary compressors.

➼ Rotary Screw compressor

Rotary screw air compressors also use positive displacement. Rotary compressors compress air compression using a system consisting of interlocking helical screws that inhale the air and then pressurize and compress it in a smaller area.

Rotary screw air compressors are one of the most common types of air compressors. Moreover, It is easier to take care of and is the more preferable choice for continuous use. They generally have industrial-sized engines.

There are two internal screws in a rotary screw air compressor. They rotate in opposite directions along with constant movements, and the air gets trapped and compressed between them.

Oil-free rotary screw devices use non-contacting carbon ring seals to prevent any oil from entering the air stream inside the oil-free air compressors. Also, the sectioned-off coolant on the other side of the seal eases the cooling process. However, these oil-free compressors typically lack the ability to throttle the inlet, which results in heat buildup over time in these types of oil-free air compressing machines. So, the flooded models are more preferred to the users who need ample supplies.

➼ Rotary Scroll Compressors

Rotary scroll compressors are considered one of the best choices among the rotary compression units. In this type of compression unit, you can find two spiral elements. one of these spirals is fixed, and the other one goes around in eccentric circles.

The inhaled air is directed towards the center of the spiral. Then this air gets compressed due to being transported inside a continuously shrinking volume. After that, the air reaches its desired pressure by going through about two to three revolutions of the rotor. And then, finally, the air is discharged.

The scroll compression technology is an advanced air compression system. It has a mobile and a stationary spiral. These two work together to bring air into the chamber for compression. The volume of the air is reduced within the spirals in order to compress the air. After that, the air is directed to the center of the compressing device to be cooled.

The most significant advantage of these scroll compressors is that the spirals never come into contact with each other. This technology eliminates the possibility of any residual friction or wearing on the working system. Some of the models of this type of compressors require lubricant or oil. But there are many models available out there that can operate without using oil.

➼ Lobe Type Air Compressors

Lobe compressors are a type of rotary air compressor. The working principle of this type of compressor is that it incorporates two intermeshing rotors rotated by two parallel shafts and each of these two rotors has two lobes. However, tri-lobe rotor designs are also available.

The air enters the displacement volume after passing the inlet. Then, it is carried towards the outlet at a constant speed and constant displacement volume. The compression occurs during each rotor passing the machine’s outlet. Timing gears are used to control the relative position of the rotors to one another.

➼ Vane Compressors

Another compressing machine that uses the positive-displacement compression system is called the rotary-vane compressor. This type of device has a similar working principle to the rotary-screw compressor. But, instead of screws, these positive displacement compressor systems have built-in rotors along with adjustable arrangements of blades.

The blades or vanes are mounted on a rotor, which is rotated inside the cavity. The air is compressed between the blade and its casing. The arms approach the air input and get elongated. This creates a large air cavity. As the motor spins and moves air with it, the arms start getting smaller and approaching the output. This creates a smaller space between the vanes and the round casing, and this reduction of space volume compresses the air. After that, the air is then moved out to a different exhaust port.

This type of compression device is able to deliver specific volumes of air at a high-pressure output. Also, it is very easy to use. This is why it’s pretty preferable among the users who need an air compressor for private projects like a home workshop and the most popular type of compressing device found in these environments.

➼ Liquid-Ring Compressors

Liquid-ring compressors can be considered quite similar to rotary vane compressors, except for the fact that their vanes are integrated with the rotor. In this type of compression unit, the compression chamber is sealed using the churning of a rotating liquid ring.

In these compressing devices, some liquid (in most cases water) enters the compressing machine and forms a ring on the inner surface of the cylindrical casing through the application of a centrifugal force. The enclosed volume between the impeller vanes and the casing changes using the eccentricity of the impeller’s axis of rotation and the casing’s geometric axis.

After entering the air compression chamber, the air gets trapped between the enclosed volume of the impeller vanes and the liquid ring. As the volume shrinks, the air gets compressed. This compressed-air then leaves the machine through the discharge port.

2. Dynamic displacement air compression

Dynamic displacement air compressors or Roto-dynamic compressors work by forcing the air into compression chambers with rotating blades and impellers power by an engine. The inhaled atmospheric air is restricted and pressurized and then stored in the air compressor tank.

Compressors with this compression process have various compressor elements like variable reciprocating pistons, valve head, connecting rods, pistons, crankshafts, eccentric rings, and cylinders.

This dynamic compression system is much faster than the alternative in completing air compressor function and providing compressed air. Furthermore, a dynamic compressor is capable of delivering a higher amount of compressed air supply.

Machines with this air compression process can mainly be considered as industrial air compressors, preferable if you are looking for an industrial compressor to use in an industrial application that requires constant pressure and large volumes of air flow. The roto-dynamic compressors are developed to be used in large projects, like to run a factory operation, a steel manufacturing industry, or a chemical plant. Many automobiles also use this technology.

Centrifugal compressors and axial compressors are examples of non-positive displacement air compression system-based compressors.

⦿ Axial air compressor

Axial air compressors have a series of turbine blades. These machines use these blades to force the air through a small area and generate air pressure. This may seem kind of similar to other bladed compressing systems, but that’s not necessarily the case. Axial flow compressors actually operate with stationary blades. Their task is to slow the flow of air and increase the air pressure in the process.

This particular type of compressing machine is not very common. Also, they have limited functionality. They can be seen usually being used in aircraft engines or large air separation plants.

⦿ Centrifugal Compressor

Centrifugal air compressors are also called radial compressors. This type of compressor uses a rotating impeller to bring the air into the center. Then this air is pushed forward or outward through centrifugal force. A diffuser is used to slow the flow of air, and thus kinetic energy is generated.

The centrifugal compressor generally uses high-speed electric motors. One of the common uses of centrifugal compressors is in HVAC systems.

Final Words

Air compressor is an essential tool in many of our daily lives. This is a handy tool with versatile applications ranging from private projects at home to professional works like a construction project or auto repair and used to operate various pneumatic tools according to your needs.

Even though compression of air is the primary task of any type of air compressor, each compressor type has been developed to be used for some specific applications. So, it is crucial to know different kinds of air compressors and how they work to figure out the appropriate one for your works.

By reading this article, you’ll learn about different types of compressors and their working principles. If you want more information, please check out our other relevant articles, and if you have any specific questions, please do not hesitate to contact us.

Thank you for reading.

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Hi, and welcome to Toolented. My name is Michael D. Sanders. I am a Mechanical Engineer by degree, who is a blogger by passion, and this combination of knowledge and passion is what brought Toolented to life. On my blog website, you will find necessary information about your needed automotive tools, reviews of your potential choices, and comparisons between different types of tools. To learn more click here.

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