TL;DR
Dust buildup on fan blades causes imbalance and reduces airflow. Clean the impeller with a wire brush, restore uniform blade geometry, and schedule more frequent cleanings if the source is upstream filtration inadequacy.
What you might see
- progressive vibration increase over weeks or months
- airflow decreasing while motor current stays the same
- visible dust coating on impeller blades when inspected
- upstream filter differential pressure below normal
Likely causes
Inadequate upstream filtration allowing airborne dust to reach the impeller
Upstream filter damaged or improperly sealed, bypassing around the filter media
Sticky or adhesive process contaminants (grease, humidity, or chemical mist) in the airstream
Cleaning intervals too long for the dusty environment
Required tools
- Wire brush or stiff plastic brush
- Vacuum cleaner
- Vibration meter
- LOTO kit
- Replacement upstream air filters (correct size)
Safety first
- Lock out and verify zero rotation before entering the fan housing. Impeller rotation can restart if LOTO is not applied.
- Some process dusts are combustible (grain, wood, metal powder). If the dust in the fan is combustible, follow your facility's hot work and confined space entry procedures before cleaning.
Procedure
- 1
Lock out the fan disconnect and verify zero rotation before opening the fan access panel.
Warning: Fan impellers can coast for several minutes after power removal. Verify the impeller has completely stopped before entering the fan housing. - 2
Take a before-cleaning vibration reading at both bearing housings and record it. This establishes baseline to compare after cleaning.
- 3
Open the fan access door. Inspect all impeller blades for deposit thickness and uniformity.[1]
- 4
Clean each blade with a wire brush or stiff plastic brush. Apply equal effort to each blade to maintain balance. Do not remove more material from one blade than another.[1]
- 5
Vacuum the housing interior to remove loose dust. Do not blow compressed air inside the housing, it redistributes conductive dust to the motor and bearings.
- 6
After cleaning, re-energize the fan and take a vibration reading. Compare to the before-cleaning reading. If vibration is still above 0.3 in/s, the impeller needs field balancing.
- 7
Inspect the upstream air filters. Replace any damaged or bypassing filters. If dust loading is high, shorten the filter replacement interval.
- 8
Document the cleaning date and the before and after vibration values in the maintenance log. Use this data to establish a preventive cleaning schedule.
Sources
Greenheck CUE Centrifugal Upblast Roof Exhaust Fan Installation and Maintenance Manual, Greenheck Fan Corporation
Greenheck CUE Utility Fan installation, operation and maintenance instructions, impeller cleaning and vibration check procedures (general)
View source
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