How to spot-check the performance of a reciprocating compressor
By Dr. Bryan Long, principal consultant – vibration dynamics and noise
There are often occasions when it is desirable to spot-check the performance of a reciprocating compressor; just after a rebuild, as part of commissioning or when something seems different.
Here are a few things you can do:
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Method, pros and cons |
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Quantification of difference in throughput | Diagnostic insight | Ease of use | ||
1 | Compare measured flow with that predicted by OEM sizing (or other) software. This is easy to do once a model has been created. Creating the model is not difficult but requires accurate load step numbers (clearances).![]() ![]() |
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2 | Compare inter-stage pressures with software model predictions![]() ![]() |
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3 |
For cylinders on the same stage, compare discharge temperatures. |
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4 |
Check for hot valves by comparing equivalent valve cap temperatures |
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5 |
Calculate the capacity of each stage separately based on observed pressures and suction temperatures and look for significant discrepancy. A model is not required but best to set up an Excel calculation (which requires gas properties). If there is a significant difference, the lower value is the more accurate result, and the other stage has a problem. |
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6 |
Detailed analysis of pressure-volume curves along with ultrasonic patterns. Well, this is not so simple; included here for comparison.
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The discharge temperature of a cylinder with a valve leak (black curve) increased, compared to another cylinder on the same stage (red), until a repair was made. |
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Suction valve cap temperatures show one significantly higher reading, indicating a leak. |
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Calculated capacity of stage 1 increases relative to stage 2 as a leak develops. The leak is verified by the rising discharge temperature deviation (black curve). |
Performance Assessment (Thermodynamic) • Machinery Condition and Performance Monitoring • Condition Monitoring and Remote Vibration Analysis •
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