Liquid Carryover in Reciprocating Compressors: Causes, Damage and Prevention

Liquid is the most destructive thing that can reach a reciprocating compressor cylinder. Gas compresses; liquid does not. A slug of condensate or water can break valve plates in seconds, and a large one can bend or break a piston rod. Even small, continuous carryover washes away the cylinder lubrication and shortens the life of rings, rider bands and packing.

Where the liquid comes from

• Suction scrubbers that are undersized, flooded, or have a failed level control or drain valve.

• Condensation in suction piping when the gas cools below its dew point, at night, in winter, or in long uninsulated lines.

• Interstage coolers that cool the gas too much, so liquid drops out before the next stage.

• Process upsets upstream that send slugs of liquid to the compressor.

• Water or chemicals left in the system after maintenance or cleaning.

Warning signs

• Valve failures that repeat on the same stage

• Knocking, or sudden changes in vibration

• Liquid at scrubber drains that drain more often than usual

• Washed, dry cylinder walls and wet valves at inspection

How to keep liquid out

1. Test scrubber level controls, high-level shutdowns and drain valves on a fixed schedule, not only when something fails.

2. Insulate or heat-trace suction lines that can collect liquid, and give them low-point drains.

3. Keep the gas leaving each intercooler above its dew point, with a margin.

4. Drain and purge the system before restarting after a shutdown.

5. When a valve fails, check the scrubber before ordering a new valve.

Short Way traces repeat valve failures and liquid problems on reciprocating compressors across Iraq. Read more on why compressor valves fail, or talk to our engineers.