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Hello all,

Do we observe high axial vibration (and more than radial vibrations) in all centrifugal fans ?

I have a case where overhung centrifugal fan driven by motor and coupled with belt drive. Following overall velocities (10-1000 Hz RMS) recorded,

Axial: 15 mm/s, Horizontal: 12 mm/s, Vertical: 8 mm/s

I have also attached spectra (freq vs RMS velocity). What are the possible faults; to me looks like looseness.

Similar cases (high axial vibration for centrifugal fans) reported earlier in this forum. I was wondering whether its machine configuration, fan operation, or common design issues (in once case it was a weak bearing block).



Images (2)
  • Centrifgual_fan_axial_fft: Axial velocity spectrum
  • Centrifgual_fan_horizontal_fft: Horizontal vibration spectrum
Tags: fan, axial, vibration

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How can we read the two spectra? There is no vertical amplitude scale, and the horizontal axis does not have good numerical and consistent values (such as 100, 200, 300 Hz) or useful small divisions. Looks like there may be 1/4 x shaft speed present that is not normal.

Axial vibration on a centrifugal fan is normally not dominant. Possible causes of high 1xSS vibration in axial direction are shaft/belt sheave misalignment, 2-plane rotor unbalance, thrust bearing damage, rotor or seal rub, loose bearing or fan base supports, or resonant structure/foundation.



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