This course explains what happens inside a reciprocating compressor cylinder by focusing on the pressure-volume diagram and the fundamental thermodynamic principles – but not in an overly academic way. Included are discussions of pressure-time and pressure-volume diagrams, capacity, power, and compression efficiency. In addition, it will cover the effects of changing conditions, gas analysis, temperature, and pulsation. An understanding of the pressure-volume diagram and the basic thermodynamics forms a good foundation for a deeper understanding of the mechanical aspects. This course would excellent for the person new to reciprocating gas compression or the veteran who needs a refresher.