High Discharge Temperature on a Reciprocating Compressor: Causes and Fixes

Discharge temperature is one of the most useful numbers on a reciprocating compressor log sheet. It rises before most mechanical problems become visible, and a high reading also shortens the life of valves, piston rings and packing. When one stage starts running hotter than normal, the cause is almost always on a short list.

Normal or high?

Every stage has an expected discharge temperature set by its compression ratio, the gas properties and the suction temperature. Compare the reading with that expectation and with the unit's own history, not with a single fixed number. A sustained rise on one stage while operating conditions have not changed deserves attention. The high temperature alarm is the last warning, not the first.

Common causes

• Leaking valves. The most common cause. Gas leaking back through a suction or discharge valve is compressed again and heats up. The cover of the leaking valve usually runs hotter than the others on the same cylinder.

• Higher compression ratio than design. Low suction pressure, high discharge pressure, or an interstage pressure shifted by a problem on another stage.

• Hot suction gas. A fouled intercooler, low cooling water flow or a fan problem on an air cooler raises the temperature going into the next stage.

• Worn piston rings. Gas leaking past the piston is compressed again and adds heat.

• Poor cylinder cooling. Blocked or scaled jacket passages, or low coolant flow.

• A change in gas composition that changes how much the gas heats up during compression.

• Instrument error. Always confirm the reading before opening the machine.

How to find the cause

1. Confirm the reading with a second instrument.

2. Compare the stage pressures with normal. If the compression ratio has risen, the cause is probably outside the cylinder: coolers, process conditions or another stage.

3. Compare the suction temperature of the stage with normal. If it is high, check the cooler upstream.

4. Compare the valve cover temperatures on the cylinder. One cover hotter than the rest points to that valve.

5. If pressures, suction temperature and valves are normal, suspect the piston rings or the cylinder cooling.

Fixing it

Recondition or replace leaking valves, and find out why they failed. Clean fouled coolers and restore cooling water or air flow. Replace worn rings. Clear the cylinder cooling passages. Where the cause is the operating point, bring the compression ratio back within the design range. After the fix, record the temperatures as the new baseline.

Short Way troubleshoots high discharge temperatures and other running problems on reciprocating compressors across Iraq. If a stage on one of your units is running hot, talk to our engineers. For more on valve problems, read our guide to compressor valve failure.