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July, 2009
MAINTENANCE MINUTE
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Welcome to the Centrifugal Blower Maintenance Minute,  
the 60 second newsletter designed specifically for centrifugal air & gas blower operators.  Each month we will feature a different aspect of service and maintenance to centrifugal blowers. We will review operation, troubleshooting, actual case histories, and answer reader questions.  
Unusual Noises in 
Centrifugal Blowers
 
BearingMulti-stage, centrifugal blowers run for years without problems.  But, eventually, someone will walk by and report "that blower sounds different, there is an unusual noise".   Then, I will get a call to come over and listen to my blower and tell me what is wrong with it.  The most common cause of unusual noises are due to air, or gas, flow.  Opening and closing the inlet, or outlet, valve will change the blower "noise".  A surging, pulsing sound, is indicative of the blower not getting enough air, or gas.  Dirty filters, plugged diffusers, broken butterfly valves, and even closed valves 'down the line' could cause surge in a blower!  Cold winter air can 'ice up' at the blower inlet and change the noise of air flow.  
Then, of course, there is the mechanical causes: bearing, coupling, or impeller, failures; loose, or broken, bolts anywhere in the blower system; and motor operations. Visual inspection is the first step to diagnosis.  I've been called to jobsites where all they had to do is remove the coupling guard to see that the coupling element had failed, or the set screws had loosened allowing the hub to move.
Noisy bearings can usually be identified with the simple screwdriver, or stethoscope, test. If you suspect a bad bearing, remove the housing cover and look at it.  A loose coupling key hitting the shaft can sound very much like a bearing noise.  Determining whether an impeller has failed, or there is foreign material inside the blower, is a little tougher to ID.  Check valve pieces can fall into the outlet housing and "rattle".  Inlets can suck up stones, washers, etc... and emit unusual noises.  If the "ticking" sound seems to be at once per rev, it could be a cracked(fatigued) impeller.  Likewise, a scraping sound could be an impeller rubbing due to axial movement of the rotor.  In landfill gas applications, chunks of built up dirt and condensate often break off and "rattle" around. 
Finally, motor noises often sound like they are coming from the blower when in fact they due to motor problems.  A single phased motor will run, usually at a lower speed, but have a sound like a once per rev scrape.  A VFD will slow the motor and have a high pitched murmur similar to a bad bearing.  Electrical noise can actually transfer through the shaft/coupling to the blower.  Sometimes the cause of the noise can only be determined by vibration analysis.  Other times, all you can do is wait until it gets worse, or goes away!!   
         
                                                              
Maintenance Minute is published each month by Snyder Technical Services, LLC and is based on the work of former Lamson National Service Manager, Bill Snyder.  Should you have any questions, or problems to discuss, please contact me. 
 
Sincerely,
 
Bill Snyder
Founder - Snyder Technical  Services, LLC 
Next Month: 
 
Oil Leaks --- Why??
Thought for Today:
 
                "Beauty is only a light switch away!"
 
 ---Perkins Library, Duke Univ, Durham, NC