What compressor types are there, and which one is right for you?

There are a lot compressor types to choose from. Choosing the right type of air compressor for your needs is very important. It will save you a lot of trouble and money in the long run. I will tell you the advantages and disadvantages of the different kinds of compressors.

Which one is right for you? I can't tell you! It all depends what you use it for! I will give you a short list with the most popular types of compressors and discuss the pros and cons of each one, including some typical uses. After reading this page, you should have a fairly good idea what kind of compressor is best for you.

All these compressor can supply about the same pressure. The difference is the output FLOW (cubic meters per minute, or cubic feet per minute). Most common pressure is 7 to 8 bars. Reciprocating piston compressors are most often seen for high-pressure / low flow applications (up to 30 bars), while rotary screw compressors are used for continuous applications.

Reciprocating piston compressor

Example of a reciprocating piston compressor.
Photo: Atlas Copco

This compressor type uses a piston, which moves inside a cylinder, to compress the air.

Reciprocating simply means 'moving back-and-forth'. Usually it's a piston that move back-and-forth, but it can also be a rubber membrane (membrane compressor).

Two sets of valves take care of the air intake and exhaust. Piston compressors are available as lubricated and oil-free, and most of the time with 2 cylinders in V-shape. Very small piston compressors use only 1 cylinder.

The piston compressor is nowadays available from 1 HP to about 30 HP (small air compressor). They are used a LOT for general-purpose applications ('workshop-air'), where the air is used for hand-tools, cleaning dust, small paint jobs, etc. Together with the rotary screw compressor, it's one of the most used compressor types.

Pros:

• Relatively cheap
• Easy maintenance (easy to understand the inner working)
• Suitable for high pressures

Cons:

• Very noisy! You really need to put this type of compressor in a sound-isolating box or in it's own room.
• High outlet temperature of compressed air
• High oil content in air piping.

More information about reciprocating compressors.

Rotary screw compressor (oil-injected or oil-free)

Rotary screw compressor element. Photo: Atlas Copco

Another one of the popular compressor types is the rotary screw compressor. It uses two rotors (helical screws) to compress the air. The rotors have a very special shape and turn in opposite directions with very little clearance between them.

Air sucked in at one end gets trapped between the rotors, and get pushed to the other side of the rotors (the pressure-side). There are two basic types of rotary screw compressors: oil-injected and oil-free. The oil-injected type is most common, because it has a much lower price-tag than the oil-free one (which you should only use if your application requires 100% oil-free air).

Pros:

• Low noise level. You can just put in in your workshop without wearing ear-protection.
• These are the work-horses of the compressors and can supply a large amount of compressed air.
• Good energy-efficiency compared to piston-type compressors
• Relatively low end temperature of compressed air
• Possible to use energy recovery

Cons:

• Purchase price is much higher than piston-type compressors
• More complex design, good maintenance very important.
• Minimal air use (per day/week) is required to prevent water condensate forming (will create a lot of problems with rust!)

More information about rotary screw compressors.

Scroll compressor

Inside of a scroll compressor. Photo: Atlas Copco

I like scroll compressors... they are 'elegant'.. They run smoothly, with almost no noise, no vibrations and use a clever design principle to compress the air. They are however one of the less seen compressor types.

How do they work? They compress the air using two spiral elements. 1 is stationary (it doesn't move), and the other one moves in small eccentric circles inside the other spiral. Air gets trapped and because of the way the spirals move, get transported in small air-pockets to the center of the spiral. It takes about 2.5 turn for the air to reach the pressure output in the center.

I haven't seen too many scroll compressors 'in the wild' (as compared to other compressor types). Normally they are used in places where a small amount of oil-free compressed air is needed (for example drinking water-treatment facilities, specialized factories or laboratories, etc). They don't product a high air flow. If you need a lot of oil-free compressed air, go for an oil-free rotary screw compressor.

Pros:

• Very quiet. Really very quiet!
• Compact. A scroll compressor is very small.
• Simple design, not so many parts
• Low maintenance (hardly any)
• Oil-free design

Cons:

• Low capacity (flow, liters/minute or cfpm).
• Relatively expensive
• When the scroll-element fails, there's a very big chance you just have to buy a whole new element.
• The compressed air gets very hot! Much hotter than compared to other types of compressors

More information about scroll compressors.

What kind of compressor is right for you?

It all depends what you use it for! Do you have any specialized needs? Do you need a lot of air, or just a little bit? Always check your tools, machines and other air-users and calculate how much air (cfpm = cubic feet per minute, you need.

If you just need a small amount of air (power some tools, operate a small machine), the most obvious choice would be to buy an oil-lubricated piston-type compressor. Do you need oil-free air? Use special filters to filter out the oil, or buy an oil-free piston-type compressor (more expensive, maintenance and repairs will also be more expensive compared to oil lubricated compressors).

Do you need more air? For example, do you use compressed air to sand-blast, spray paint, operate one or more machines that use a lot of air, then the obvious choice would be a rotary-screw compressor. They range from small (5 kW) to very big (1000 or more kW).