This document summarizes different types of air compressors, including reciprocating compressors that use pistons moving back and forth inside cylinders, rotary compressors that use rotating parts to compress air, and positive displacement compressors like roots blowers, vane pumps, and screw compressors. It provides details on how centrifugal compressors work by adding kinetic energy to airflow and briefly describes applications of roots blowers and rotary vane pumps. The document concludes by noting how rotary screw compressors are commonly used for large industrial applications requiring high air pressures and volumes.