Machines that add energy to gases and vapors — raising pressure and driving flow. The practical boundary with blowers and fans is the pressure ratio: above ~1.2 the service is a compressor's and gas compressibility dominates the design (discharge temperature becomes a process and integrity variable).
Working principles
(principles as their own notes and handbooks in Phase 1)
- Positive displacement — discrete gas volumes are trapped and compressed:
- Reciprocating: piston (API 618), diaphragm — high ratios per stage, pulsating flow;
- Rotary: screw (dry/flooded), vanes, scroll, Roots (lobes), liquid ring.
- Dynamic — energy transferred continuously by a rotor (API 617): centrifugal (the most common in process service), axial (high flows) and mixed flow.
The working fluid is an attribute of the service, not a taxonomy level: vapor compressors (centrifugal, screw, piston) are the backbone of industrial refrigeration and follow the same principles.
Reliability: in reciprocating machines, compressor valves and rods/packing dominate; in dynamic machines, gas sealing (dry gas seals), bearings and surge — the unstable boundary of the curve.