A two stage reciprocating air compressor is ideal for demanding, industrial applications. They are much tougher than single stage compressors and can handle more pressure and more capacity (cfm).
Two stage air compressors
With two stage air compressors, the air is compressed in two stage. In between the stages, the air is cooled.
Air is compressed to medium level. This is the big cylinder/piston. It moves a high volume of air, but at a low pressure.
Air is cooled back to a much lower level. This makes the compressor more efficient and reduced stress on the high pressure stage.
The air is compressed further to the end pressure. This is the small cylinder/piston. It moves a lower volume of air, but at an high pressure.
On some models, you can clearly see the two stages (a v-shaped pump with a big and a small cylinder). On other models, they low pressure and the high pressure cylinder are cast in 1 block. It looks like a single stage compressor, but it is a two stage compressor.
Two stage air compressors can get up to to 175 psi (12 bar). You need to figure out for yourself how much pressure you need. If you only need 125 psi, it's better to look for compressor with a lower maximum pressure, but at an higher capacity (cfm): more air for your bucks!
Like with buying any type of compressor, you need to know (approximately) the amount of air that you will be using.
If you don't know what capacity you need, be sure to start at the air compressor buying guide main page. Two stage reciprocating air compressors go up to about 50 CFM (cubic feet per minute). If you need more, a rotary screw compressor might be a good option.
Other things to know when buying a two stage compressor
The duty cycle of almost all two stage air compressors is 100%. That's one of the reasons why they are viewed as 'more powerfull' and durable. 100% duty cycle means that the compressor can run non-stops, without needing time to cool down.
In contrast, most single-stage air compressors have a duty cycle of 50% or 75% (see single stage air compressor buying guide)
Since two stage are compressors are a lot bigger than single stage air compressor, the right electrical connection becomes important. Make sure that you have an adequate power supply available at the place where you want to install your compressor. Have it installed by an electrician when necessary.
Some compressors can be bought either with a single fase or 3-phase motor. And often you can choose between 200 volts, 230 volts or 460 volts. Make sure you choose the correct type for your situation.
Bigger two stage compressors only come as 3-phase machines. Keep in mind that most dual stage air compressors come without any wiring, so you have supply that too.