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April 2014 · Energy-Tech Magazine
June 2012 Go to Page 1 2 3
Detectable problems in compressors
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Note: Impact damage to dynamic compressor blades or impellers can mimic compressor fouling. If performance does not recover after washing, then the unit should be inspected for internal damage.

Many units are equipped with boroscope ports that facilitate internal inspection with minimum downtime and disassembly.

Additionally, reciprocating compressor fouling (due to either debris or liquids in the gas) might result in damage to the suction or discharge valves and the piston rod. Damage to the valves will manifest itself as an increase in temperature of the valve covers. Rod damage might be detected during operation as non-linear movement of the rod as it passes through the gland at the crosshead-cylinder interface. Also, the wear pattern will become more severe as the rod wears against the packing.

Corrective action

  • Disassemble valves, clean and replace valve plates as necessary
  • Remove piston and rod assembly and replace rod.

Loose piston

/>The installation of the piston rod onto the piston is a delicate procedure requiring a special lubricant, special technique and often special tools. If not properly installed, the piston might become loose on the piston rod. This will result in the piston hitting the end wall at the head-end and crank-end of its travel, and eventually will result in failure of the piston end wall.

Corrective action

  • Pull the head-end cover and head-end and crank-end valves to inspect the piston
  • If no damage is evident, re-torque the piston rod nut, re-assemble the compressor and test
  • Replace damaged components as necessary

Bearing clearance (Hydrodynamic bearings)
Excess bearing clearance can result from improper bearing installation or from journal and bearing shoe wear during a period of time. In either case, the effect of bearing looseness can be detected during operation by checking the bearing whirl orbit.

Hydrodynamic bearing whirl orbits should be checked at the factory as part of the unit run test (where the necessary vibration equipment is most likely to be available). At the factory this problem is relatively easy to fix.

An unstable orbit will also demonstrate high vibration. However, the vibration might or might not be above maximum allowable limits. Continued running with an unstable orbit will lead to increases in vibration that will eventually exceed acceptable limits and, therefore, should not be ignored.

Reciprocating compressor valves
Due to the stresses on the valve plates during normal operation, suction and discharge valves are the high maintenance items in reciprocating compressors. Valve plate failure will have a negative impact on compressor performance. Gas path analysis, coupled with direct measurement of the valve cover temperature, is the easiest way to detect valve plate failure.

Corrective action

  • Periodic gas path analysis to monitor compressor performance is the first step in detecting a problem.
  • When degraded performance is detected, a check of valve cover temperature can isolate the problem valve or valves.
  • Replace the defective valves as soon as possible.

Entrained liquids
Liquids in the gas present a major problem for reciprocating compressors. At a minimum they will result in early and frequent failure of the compressor valves, and when extreme can result in one or more bent rods. Liquids do not present as big a problem for dynamic compressors, screw compressors or blowers since these compressors are more tolerant to liquids in the gas. In fact, the screw compressor is so tolerant of liquids that sealing oil is intentionally injected into the gas stream (as in oil flooded screw compressors) prior to compression and extracted after compression.

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