6.4 VIBRATION. Vibration of fans is a symptom of another problem.
Vibration may be caused by:
Poorly aligned bearings, couplings, or drive
Weak or inadequate foundation
Loose set screws on fan-to-shaft connection
Loose bolts on bearings
If items a through f above are not apparent causes, the wheel balance
must be checked. Make sure that the fan blades are clean. Check for static
imbalance as follows:
Run the fan for 10 minutes to bring the lubricant to operating
Shut the fan down.
Block off fan inlet or outlet to prevent fan rotation due to air
Lock out the electrical supply.
Disconnect the motor (belt driven fans).
Give the fan wheel a vigorous rotation by hand, and mark the part of
the fan which stops at the top.
Repeat, alternating the direction of the rotation. Continue
repeating until a definite pattern becomes apparent.
Add a metal weight at the light point on the wheel, and test again.
If no static unbalance is apparent, or if a satisfactory balance can be
produced with weights, the fan wheel may have a dynamic unbalance. A
balancing contractor or the manufacturer should be contacted to correct a
dynamic unbalance. Table 6-l shows a summary of fan problems and remedies.