Mechanical 

        

Problem 

    

Possible Cause

   

Recommended Action
General Fan Noise    The fan could be running in stall.    Check the actual fan performance against the fan curve to determine where on the curve it is operating.  If it is to the left of the peak pressure point the fan is generally in stall.  If in stall see if the ductwork can be modified to eliminate high pressure loss sections. Low amps could indicate the fan is in stall.  Reduce the pitch angle. 
    
Bearing noise varying from a 'dry' rumble to a squeal    Improper greasing   Check the bearings are packed with the correct grade and amount of grease.  If the bearings are of the sealed-for-life type replace them.
    
    The bearings may be loose on the shaft or bearing support   Tighten the adaptor sleeve or collar
   
    The bearings have not been properly tensioned   Re-tension as required
   
Rough lumpy sound   The bearings may have brinelled.  Brinelling occurs when the fan is vibrated during transit or through ground vibrations when stored.  This causes the bearing to vibrate at a single point and therefore indenting the bearing race.  Problems with brinelling usually occur shortly after a fan is installed.   Replace the bearings.  To Avoid brinelling the fan impeller should be rotated frequently, at least daily.
   
    Excessive belt tension   Check and adjust the belt tension
   
Shaft seal squeal       The seals may have dried out.   The seals may require lubrication or may be misaligned.
   
Air noise   Air noise can be generated from a number of sources such as grilles, bends, badly designed duct fittings, excessive duct velocities etc   Check the duct design is such it does not generate turbulence and therefore noise.  An attenuator may be needed to resolve the problem.
   
Vibration   The impeller may be out of balance.   Site balancing may be practical but, if not, remove the impeller and balance.
   
    The shaft may be bent.   The shaft will have to be replaced.
   
    Impeller may be worn as a result of handling abrasive or corrosive materials   The impeller will have to be replaced
   
    Material such as dust or grease could be sticking to the fan blades.   Clean the impeller blades.  This should be done on a regular basis if dust and/or grease are constantly present in the air being handled.
   
    The impeller may have been damaged by loose material in the duct system.   Depending on the level of damage the impeller may have to be replaced.
   
    Noise being transmitted through the building structure   Check vibration isolators have been fitted and, if fitted, check they are correctly positioned.  Vibration isolators are fitted but not strong enough.  If bottoming, adjust if possible or replace with more suitable mounts.  Fit flexible connectors between the fan and ductwork.