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 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.
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 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.
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
Do you need guidance on what air compressor type would work best in your facility?
We can send a team to your site and find out your exact requirements, highlight existing efficiencies and give you a list of alternative solutions which might include differen types of air compressor.
Request a FREE consultation from us by filling this form.
You could also call one of our sales representatives directly.
Ask them to guide you on how to use our selection of calculators to measure your on-site conditions and determine equipment specifications.
Get in touch!
What is the difference between an air compressor and air blower?
Air blowers and air compressors are both used to pump air in order to do work. And they use similar mechanics. The difference is that blowers don’t compress air. They move the air internally and apply kinetic energy to increase the velocity of the air. The simplest example of a blower is a tabletop fan. However modern-day blowers can generate pressure up to 1000 mbar (1barg) and there are multiple technologies used to achieve this. Please contact Atlas Copco team for more details on blowers and blower applications.
What is the advantage of using compressed air as a source of power?
There are multiple advantages to consider, depending on how you look at it. Relying on compressed air reduces the risk of electrical hazards. Tools built to use air tend to weigh less than electrical tools. Air compressors are more mobile than electrical outlets and generators. In most cases the initial purchasing cost of air-based tools is more than electric or hydraulic tools, however the advantage of flexibility and increased productivity overcomes easily the little extra paid for a pneumatic tool. Moreover, air distribution systems are easier to install and user friendly when compared to electrical grids and hydraulic systems. Air cannot damage or overheat the internal mechanics of the tools. And air tools run with less expended heat therefore easier to handle and manage by the users.
Which industries require air compressors?
Air compressors are one the most common pieces of equipment in any industry. There are too many uses to name them all. Here are a few examples: Spray painting, filling air in tires, supplying air during medical procedures, filling air in packaging, producing goods in food & beverage, running farm equipment, running power tools, pneumatic conveying, aeration, mixing of products etc.
What voltage do I need to run my air compressor?
That will depend on the size of compressor that you need for your facility. There are small piston type compressors that are good for home use - they can be run on 110/220V. And then there are larger models that go up to 680V and the very large ones operating at 11,000V. If you aren’t sure about what size of compressor you need then it’s best that you get in touch with Atlas Copco for our FREE Energy Efficiency Audit.
How much air pressure will my tools and equipment need?
Again, it depends on the type of work you’re doing, and you should get in touch with Atlas Copco to give you an audit that will correctly assess your needs. Most basic air tools require about 70-100 PSI and consume less than 10 CFM. It will help you to consult the manual and documentation that comes with your tools and machinery.
How regularly will my air compressor need servicing?
These are variables that change from one user to the next. Your work will require you to run the air compressor a certain number of hours in a day. We can’t tell what that amount is. With periodic usage in a day an annual service will be enough to cover you. But if your air compressors are running continuously through the day that it’s likely that you will need something like a quarterly service.
How often does the oil in my air compressor need to be changed?
This applies only to Atlas Copco oil-injected type compressors. We recommend that you change the oil every 3 months at minimum. For some compressors like rotary screw compressors we’d recommend changing oil every 4000-8000 hours of use. This is subject to the recommendation listed in the documentation that comes with the machine.
How do I make sure my compressed air is free from contaminants?
The most common contaminant comes in liquid form - a combination of condensate and oil. Water and oil can carry bacteria and dirt. You’re going to need an air drying and filtration system attached to the air compressor. When you set up a Free Premium Energy Audit with Atlas Copco, we can guide you on what type of system you will need.
