4 Main Types of Air Compressors for Industrial Facilities

Learn about the four main air compressor types, their advantages and disadvantages over each other, and how to pick the right one according to your requirements.

Air compressor types and why they’re used

Air Compression is a technology that’s been in use since the practice of metallurgy began around 3000-1500 B.C. The earliest devices were manually operated. Several hundred years later the manual devices were replaced with mechanical systems that added a degree of automation to the process. By the late 1800s air compressor systems had become electrically powered and were used to deliver pneumatic energy. Since then we’ve benefitted from multiple advancements in air compressor design and a diverse range of air compression solutions.

Let’s see what are two types of air compressors from which all commercially available air compressors are derived. They are Dynamic Compression and Positive Displacement Compression.

And from these two compressor designs we have 4 main air compressor types. They are :

Axial Flow Compressrs (Dynamic)
Centrifugal Comressors (Dynamic)
Reciprocating Compressors (Positive Displacement)
Rotary Compressors (Positive Displacement)

Dynamic Compression Type Compressors

This

This type of air compressors rely on a phenomenon in fluid dynamics called Bernoulli’s principle. The principle states that as the velocity of a fluid increases the pressure exerted by that fluid decreases. What that means in practical terms is that a slow-moving fluid exerts more pressure than a fast-moving fluid - they have an inversely proportional relationship.

It’s the reason why airplane wings are designed the way they are. As the wing cuts through air the curvature of the wing causes air to flow over the top of the wing at a higher speed than how it flows beneath the wing: the higher speed creates lower pressure over the top of the wing. The difference in the lower pressure at the top and the higher pressure at the bottom produces lift. And lift is produced because gases always move from areas of high pressure to areas of low pressure.

an axial compressor is a type of dynamic compressor

An axial flow compression system looks and functions almost exactly like the turbine of a jet engine. Air enters the system through the intake and passes through rows of rotating blades arranged axially as it is compressed (Bernoulli’s principle) and moved along the shaft. The axial flow of air is then discharged at the opposite end of the shaft. The Axial compressor’s advantage is that it produces higher flow rates of compressed air compared to the centrifugal or radial flow design.

graphic showing a centrifugal compressor

In centrifugal compressors the air flows radially outward from the blades, and not along a shaft. Air enters the system through an inlet at a 90-degree angle perpendicular to a fast rotating disc. The disc is lined with curved blades that redirect the air flow along the face of the disc radially outward. The rotating disc increases the speed of air (Bernoulli’s principle). The air trapped between the curved blades is at a lower pressure relative to air in the inlet. This pressure difference creates compressed air flow and the compressed air is guided towards a discharge chamber. The Centrifugal compressor’s advantage is that it produces higher discharge pressures when compared to Axial compressors, but lower flow rates.

Positive Displacement Compression Type Compressors

This

This type of air compressors rely on a phenomenon in fluid dynamics called Boyle’s law. Boyle’s Law states that for a fixed mass of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. This means that pressure exerted by a gas within a chamber increases as the size of the chamber decreases.

This partly explains how our lungs work. Our lungs and chest cavity expand when we inhale. Since the size of the chest cavity increases the pressure inside the lungs decreases. And gases flow in the direction of high pressure to low pressure so this facilitates the drawing in of the breath. It works the opposite way when we breathe out.

From this principle of Boyle’s Law were derived two air compressor designs: the Reciprocating Compressor and the Rotary Compressor.

In a In a In a In a reciprocating compressor, a volume of air is drawn into a chamber through a valve. A piston element retreats from the valve and creates more volume in the chamber, which then causes the pressure in the chamber to decrease (Boyle’s law). Air moves in from the area of high pressure outside the chamber to the area of low pressure within the chamber. Once the piston is fully retreated it begins its advancing stroke which effectively decreases the volume of the chamber. By decreasing the volume of the chamber, it raises the pressure exerted by the air within the chamber (Boyle’s Law). As the piston completes its advancing stroke the compressed air is discharged at high pressure through an exit valve. The advantage of basic In a In a In a reciprocating compressor, a volume of air is drawn into a chamber through a valve. A piston element retreats from the valve and creates more volume in the chamber, which then causes the pressure in the chamber to decrease (Boyle’s law). Air moves in from the area of high pressure outside the chamber to the area of low pressure within the chamber. Once the piston is fully retreated it begins its advancing stroke which effectively decreases the volume of the chamber. By decreasing the volume of the chamber, it raises the pressure exerted by the air within the chamber (Boyle’s Law). As the piston completes its advancing stroke the compressed air is discharged at high pressure through an exit valve. The advantage of basic In a reciprocating compressor, a volume of air is drawn into a chamber through a valve. A piston element retreats from the valve and creates more volume in the chamber, which then causes the pressure in the chamber to decrease (Boyle’s law). Air moves in from the area of high pressure outside the chamber to the area of low pressure within the chamber. Once the piston is fully retreated it begins its advancing stroke which effectively decreases the volume of the chamber. By decreasing the volume of the chamber, it raises the pressure exerted by the air within the chamber (Boyle’s Law). As the piston completes its advancing stroke the compressed air is discharged at high pressure through an exit valve. The advantage of basic In a In a reciprocating compressor, a volume of air is drawn into a chamber through a valve. A piston element retreats from the valve and creates more volume in the chamber, which then causes the pressure in the chamber to decrease (Boyle’s law). Air moves in from the area of high pressure outside the chamber to the area of low pressure within the chamber. Once the piston is fully retreated it begins its advancing stroke which effectively decreases the volume of the chamber. By decreasing the volume of the chamber, it raises the pressure exerted by the air within the chamber (Boyle’s Law). As the piston completes its advancing stroke the compressed air is discharged at high pressure through an exit valve. The advantage of basic In a reciprocating compressor, a volume of air is drawn into a chamber through a valve. A piston element retreats from the valve and creates more volume in the chamber, which then causes the pressure in the chamber to decrease (Boyle’s law). Air moves in from the area of high pressure outside the chamber to the area of low pressure within the chamber. Once the piston is fully retreated it begins its advancing stroke which effectively decreases the volume of the chamber. By decreasing the volume of the chamber, it raises the pressure exerted by the air within the chamber (Boyle’s Law). As the piston completes its advancing stroke the compressed air is discharged at high pressure through an exit valve. The advantage of basic reciprocating compressor has over rotary compressors is that they are the most economical and relatively inexpensive type of air compressor and relatively easy to maintain. They are the go-to choice for small projects, machine shops, body shops, tire shops and small manufacturing facilities.

With

With rotary compressor, a volume of air is drawn into a chamber through an inlet or a valve. A rotating element like rotary screws, vanes or lobes sit within the chamber. The rotating elements are designed to move in a way that increases and decreases the available volume in the chamber for the air. For example, in the rotary screw design the air enters the chamber but then finds itself caught between the spiral rotor blades of the screw element. The volume of space between the spiral rotor blades decreases causing pressure to increase (Boyle’s Law). The air is compressed and directed along the grooves of the screw element at high pressure till it is discharged. The advantage with rotary compressors is that they produce a continuously high flow rate while maintaining relatively small exterior dimensions. They are a more expensive but a better long-term investment. They allow for more up-time, better energy efficiency, higher air quality, longer lifespan and are cost-effective in the long-term.

How to pick the right type of air compressor for you?

Now you know all the major air compressor types and while choosing the right type of compressor, you should ask yourself these questions:

What is the application
How much flow does my facility/workshop use
What pressure is needed within the facility
Do I need clean/dry air (use of dryer and filters)
How many hours per year does my compressor operate
How many shifts do I run per day
Is there fluctuation in flow demand between shifts (if so, a VSD compressor could be a good option and offer great savings)
Are there any plans for future expansion