TL;DR
Fan vibration is usually an imbalanced or damaged blade, inconsistent blade pitch angle, or worn gearbox bearings. Inspect blades, verify all pitch angles are equal, and check gearbox oil level and bearing condition.
What you might see
- elevated vibration felt on tower structure
- visible blade wobble or runout
- increased noise at fan speed
- accelerated bearing wear in gearbox
Likely causes
Imbalanced fan blades from scale buildup, impact damage, or blade pitch mismatch
Worn or failing gearbox bearings transmitting vibration to the fan hub
Loose blade mounting hardware allowing individual blade movement
Driveshaft misalignment or worn driveshaft couplings
Required tools
- LOTO kit
- Angle gauge or protractor
- Torque wrench sized to blade mounting bolts
- Vibration meter
- Gear oil (Marley-approved grade from nameplate or service manual)
Safety first
- Lock out the fan motor before entering the plenum or touching any rotating component.
- Inspect blades carefully for cracks before re-energizing. A failed blade inside the plenum will cause catastrophic structural damage.
Procedure
- 1
Lock out the fan motor and gearbox before entering the plenum.
Warning: Never enter a cooling tower plenum with the fan capable of energizing. - 2
Inspect each fan blade for cracks, bends, impact damage, or uneven scale deposits. Replace any cracked blade immediately.[1]
- 3
Measure the pitch angle of each blade with a protractor or angle gauge. All blades must be set to the same angle per the Marley specification on the tower nameplate.[1]
- 4
Tighten all blade mounting bolts to the torque value in the Marley service manual. Use a torque wrench.
- 5
Check the gearbox oil level through the sight glass or dipstick. Add approved gear oil if low.
- 6
Rotate the fan hub by hand and feel for roughness or looseness in the gearbox bearings.
- 7
Inspect the driveshaft couplings for wear, looseness, or missing hardware.
- 8
Re-energize the fan and take a vibration reading at the gearbox housing. A velocity above 0.2 in/s on a cooling tower fan warrants further investigation.
Sources
Marley NC Cooling Tower User Manual, Marley Cooling (SPX Cooling Technologies)
Marley NC Cooling Tower Installation, Operation and Maintenance manual, fan blade adjustment and gearbox maintenance (general)
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