How well a machine does that decides its efficiency. How well it keeps doing it decides its lifetime cost.
The two dominant rotary technologies solve sealing in opposite ways.
A screw compressor seals on clearance. Two precisely machined rotors mesh inside a casing with gaps measured in micrometres. Nothing physically holds those gaps — they exist only as long as the bearings hold their tolerance, including the thrust bearings that fight the axial force pressurised air exerts on the rotors. The seal is only ever as good as the bearings' precision on the day you check.
A rotary-vane compressor seals on a film. Blades slide in and out of a rotor and ride against the stator wall on a continuous hydrodynamic film of lubricant. The film is the seal. Under pressure the oil's viscosity rises so it can't be squeezed out, and it reforms on every rotation.
That distinction sounds academic. It isn't. A clearance is a fixed gap, and a fixed gap can only open over time. A film is a self-correcting layer that renews continuously. One has a wear path; the other doesn't. Everything in the rest of this series follows from that single choice.
The full mechanism, with independent sources →
→ https://www.linkedin.com/pulse/why-screw-compressor-efficiency-declines-over-time-rotary-contaldi-usqkf/