Single Stage vs Two Stage
Single Stage and Two Stage Air Compressors
When choosing your compressor, besides the volume of air you need (CFM), you need to determine how much pressure your application will require. Most air tools will need somewhere between 80-90 psi, but there are definitely applications requiring more.
Outside of special, high pressure air compressors, there is basically a choice between single and two stage. Very simply, single stage air compressors will give you up to 135 psi with some as high as 150 psi. Two stage air compressors will produce up to 175 psi.
Single Stage Air Compressors
Single Stage air compressors can have one single piston, or many pistons, but they will all be the same size. The more pistons, the more volume (CFM) the compressor can produce, but the pressure remains the same. Single Stage air compressors are great for home shops or even a one man automotive shop that uses 1/2" or smaller impacts.
Two Stage Air Compressors
Two Stage compressors, have at least two pistons, and they will be two different sizes. There is at least one larger piston (low pressure) and one smaller piston (high pressure). It is very common to have multiple pistons, but they will be just two different sizes. Your gain with a two stage air compressor is higher pressure. That happens with the air first being compressed in the larger cylinder, then that same air goes through an intercooler to the smaller cylinder where it is compressed again producing the higher pressure. Two stage air compressors usually are larger, with exceptions than single stage so they can handle larger volume automotive and body shops to industrial applications depending on the CFM demand.