As the names indicates, the difference between the two is the number of stages the air goes through while being compressed.
Single Stage Air Compressor
As the compressor sucks in the air, the trapped air is compressed in a single stroke with a pressure of roughly 120 psi. The compressed air is then able to move on to the storage tank (unless filtered first). Since the air is only being compressed once, the single-stage piston requires less energy to run unlike the two-stage models.
Two Stage Air Compressor
It is also known as the dual storage and it bears some resemblance to the single stage compressor process. However, the variation is that the compressed air does not go to the storage tank. It goes to a smaller piston for the second stroke at 175 psi, then to the storage tank. Since this second action is needed, less CFM (Cubic Feet per Minute) is produced.
How to determine which Air Compressor you need?
There is no one air compressor to meet all needs. You need to look at factors such as required PSI, CFM, and cost.
The single stage compressor will not have the power to run handheld pneumatic tools exceeding 100 psi. However, it would be able to produce more CFM do to the fact that the air is only be compressed once. It is used at auto shops and where minimal power is needed to run machinery.
Two stage air compressors have the ability to produce a higher PSI making them ideal for continuous uses large-scale operations. Additionally, the compressed air produced by a two stage air compressor typically runs several degrees cooler. Although apples to apples, the single stage counterpart will produce more CFM, there are larger two-stage air compressor models available to meet any CFM demand. They are also quite expensive making them ideal for workshops and factories compared to private uses.