What is the difference in a Single Stage and a Two Stage reciprocating air compressor?

The difference between a Single Stage and a Two Stage compressor is determined by how many times the air is compressed in a stroke before being sent to the receiver tank.  

A Single Stage compressor will compress the air one time to 135 psi and then it is sent to the air tank. 

 

A Two Stage compressor will compress the air once, then send that air to a smaller chamber to compress the air a second time to reach a higher pressure (175 psi), before sending it to the air tank.