What is compressor surge and how is it prevented?

Surge occurs in centrifugal/axial compressors when flow drops below the minimum stable flow, causing flow reversal and violent pressure oscillations. It damages seals, bearings, and impellers. Prevention: anti-surge control system that maintains flow above surge limit by recycling gas or opening a vent. Surge margin (typically 10-15% above surge line) accounts for control system response time. Surge detection uses flow/pressure measurements to calculate proximity to surge, triggering protective action.