Stage refers to the number of times intake air is compressed in a pump. A single-stage compressor compresses intake air one time before sending the air into a storage tank. Single-stage compressors are a good choice for individual users. Two-stage compressors compress air two times before sending the air into a storage tank. Two-stage compressors are much larger machines designed to be used by multiple users simultaneously because of their higher SCFM output and maximum working pressure of 175 PSI.