What method is used to prevent surge when dead head occurs?

• A. Spill back
• B. Open a bypass to atmosphere
• C. Increase suction pressure by valve
• D. Stop the compressor

Answer: (A)

When a compressor approaches dead head, maintaining a stable flow is essential to avoid surge. The method used to prevent surge is to send some of the discharge gas back to the suction side, creating a spill-back loop. This recirculation keeps the inlet flow above the surge limit and reduces the pressure ratio across the impeller, stabilizing the operating point so surge doesn’t occur.

Opening a bypass to atmosphere would vent gas and waste product without stabilizing the flow. Increasing suction pressure with a valve doesn’t reliably prevent surge, as the critical factor is maintaining adequate flow rather than just pressure. Stopping the compressor eliminates operation but doesn’t prevent surge during startup or transient conditions.