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June 2012 Go to Page 1 2 3
Detectable problems in compressors
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Equation 1

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Extremely large amounts of liquids can result in dynamic compressor surge.

Corrective action
The first line of defense against liquids is a scrubber or knock-out vessel. This vessel is simply a large area with a coalescing media installed upstream of the compressor, where gas velocity is reduced to allow the liquid to separate from the gas. Scrubbers are also installed between stages in multistage compressors.

Where liquid carryover is severe, a cyclone separator might be employed. A cyclone separator utilizes internal passages and the gas velocity to create vortex separation.

In addition to a scrubber line, tracing or heating might be employed to raise the gas temperature and vaporize the entrained liquids

Variable volume pocket plug
The variable volume pocket plug is positioned via a screw mechanism. Failure of the screw mechanism (see Figure 5) could result in the inability to reposition the plug. Screw failure could also result in the plug being sucked into the cylinder where it can become wedged, resulting in catastrophic failure (see Figures 3 and 4).

Corrective action
Whether the screw is turned manually or is automated via an electric or hydraulic motor, this mechanism should be inspected periodically and maintained per the manufacturer’s recommendations.

Lubrication oil
Lubrication oil should be checked periodically for lubricity, contaminants and water. For small compressors, the unit should be shut down and the oil replaced. For compressors with large volume reservoirs, the lube oil can be reconditioned on-site while the compressor is operating.

Lubrication oil should be stored correctly in closed containers in a rain protected shelter. Figure 6 shows a failed bearing shoe. The failure was the result of rain water accumulating in the lube oil storage drums and then being introduced into the compressor lube oil reservoir during periodic maintenance.

A note of caution: The photographs used are taken from actual projects. Therefore, the reader might recognize the manufacturer of the equipment shown in these photographs. However, the problems discussed are not uncommon and may involve any manufacturer’s equipment. The reader should not assume that these problems are attributable to a specific manufacturer.

Reprinted by special permission of The Fairmont Press Inc., 700 Indian Trail, Lilburn, GA, ( from Compressor Handbook: Principles and Practice, by Tony Giampaolo. This article was excerpted from Chapter 11, Detectable Problems.

Tony Giampaolo, president of Power & Compression Systems, has more than 40 years of experience in the selection, installation, commissioning, operation and maintenance of rotating equipment and equipment controls for both on- and off-shore environments. His most recent effort has been the design and installation of Predictive Emissions Monitoring Systems (PEMS) for several gas turbines and gas engines; and the design and installation of a load sharing and surge control system for three compressors operating in parallel (one electric motor driven reciprocating compressor and two gas turbine driven centrifugal compressors). He is a Registered Professional Engineer (California, Florida and Nevada), a graduate of The University of Connecticut (MSME) and The Catholic University of America (BME). Giampaolo has served as chairman of the Orange County Chapter of the California Society of Professional Engineers (at that time the second largest chapter of NSPE in the U.S.), and the technical editor (Engines-Compressors-Turbines) for Western Energy Magazine. You may contact him by e-mailing

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