Compressor Vibration

Nonsynchronous Instability of Centrifugal Compressors

Paper No. 26

J. C. Wachel, ASME Paper 75-PET-22, 1975 .

The increased use of flexible shaft centrifugal compressors has resulted in an increase in instability vibration problems, particularly in high pressure applications where the aerodynamic effects are significant. Nonsynchronous instability vibrations can occur in any machine unless careful consideration is given to all the factors that cause this type of vibration problem. This paper discusses these factors and presents actual field instability vibration data obtained in three case histories. Data analysis and presentation techniques are described which allow a better understanding of the characteristics of nonsynchronous instabilities. Using the instrumentation and techniques described in this paper, the onset of instability of a machine can sometimes be anticipated and remedial action taken before unbounded vibrations occur. The documentation of instability characteristics for several machine modifications, including bearing span, bearing type, seals, impellers, etc., shows that present analytical techniques are not adequate to predict the observed phenomena.

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