TL;DR
Vibration above 0.3 in/s on an industrial fan is usually an imbalanced impeller or worn bearings. Take a vibration spectrum reading, clean the impeller, and re-balance if needed. Replace bearings if the spectrum shows subsynchronous noise.
What you might see
- vibration level above 0.3 in/s at the bearing housings
- audible rumble or knock at running speed
- elevated temperature at the bearing housing
- loose fasteners on the fan housing from chronic vibration
Likely causes
Material buildup on one or more impeller blades causing rotational imbalance
Worn drive-end or non-drive-end bearings producing broadband vibration
Coupling misalignment between the motor and fan shaft
Loose impeller hub set screw allowing the impeller to shift on the shaft
Required tools
- Vibration meter (velocity, in/s)
- Wire brush and scraper for impeller cleaning
- Torque wrench for impeller set screw
- LOTO kit
- Field balancing equipment or contract balance service (if needed)
Safety first
- Apply LOTO and verify zero rotation before entering the fan housing or touching the impeller. Fan impellers can restart if LOTO is not applied.
- Never attempt to clean or work on a spinning impeller. The blade edges can cause severe injury.
Procedure
- 1
Lock out the fan disconnect and verify zero rotation before accessing the fan interior.
Warning: Never enter the fan housing or touch the impeller without confirming LOTO is applied and the impeller has completely stopped. Belt-drive fans can coast for minutes after power is removed. - 2
Take a vibration velocity reading at the drive-end and non-drive-end bearing housings using a handheld vibration meter. Record the readings and compare to the 0.3 in/s limit.[1]
- 3
Open the fan access door and inspect the impeller blades for material buildup, debris, or physical damage. Even a small asymmetric deposit can cause significant imbalance on a high-speed impeller.
- 4
Clean the impeller with a wire brush or scraper. Clean each blade to the same depth and do not selectively clean one side only.
- 5
Check the impeller hub set screw for tightness. Retighten if loose.[1]
- 6
Re-energize the fan and re-take the vibration reading. If vibration drops to within spec, the imbalance was material buildup.
- 7
If vibration remains above spec after cleaning, arrange a field dynamic balance or remove the impeller for a shop balance.[1]
- 8
If the vibration spectrum shows broad noise at sub-synchronous frequencies, the issue is a worn bearing. Replace both bearings at the same time.
Sources
Greenheck CUE Centrifugal Upblast Roof Exhaust Fan Installation and Maintenance Manual, Greenheck Fan Corporation
Greenheck CUE Utility Fan installation, operation and maintenance instructions, vibration limits and impeller inspection procedures (general)
View source
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