Evaluating the strengths and weaknesses of the most common online condition monitoring technologies
PROGNOST Systems’ failure mode survey of most common reciprocating compressor failure modes shows valve failures among the most frequent root cause for unplanned compressor shutdowns. New valve designs and improved materials have been introduced in the past 10 years and have reduced the percentage significantly. However, for many compressor operators valve monitoring is a main concern when evaluating condition monitoring systems to reduce unplanned downtime.
While the high percentage against other machine failures calls for further improvement, valve leakages in an early stage are usually not safety relevant. Undetected suction valve failures might lead into a complete loss of compression causing more dangerous failures, e.g., seizing cross-head wrist pins resulting from missing rod load reversal. In the early days of reciprocating machine monitoring, maintenance strategies were mainly based on temperature measurement. Today, different methods of online condition monitoring can be applied to create precise diagnostic information of the valves and other components. By comparing strengths and weaknesses of temperature monitoring with cylinder acceleration vibration measurement and pV diagram analyses, this article provides a decision making guideline to identify the best suitable permanent monitoring technology for a specific compressor.
Description of the methods
Highlighting these completely different methods, it becomes obvious that valve monitoring can be improved regardless whether it is delivered with a new machine or retrofitted to an existing machine. In any case, it is the main objective to detect a leakage of a valve that is causing a loss in efficiency of the compressor. Other damages such as broken valve springs or cracks in the valve plate or rings are considered as early stages of a leaking valve.