Yellow Logo

February, 2010
MAINTENANCE MINUTE
Newsletter 
Join Our Mailing List
Featured item this week:
Alignment Shims
Shims 

Competitive Pricing! 
GET YOUR FREE QUOTE  TODAY!
 
 
 
Blowers to Sell?
Free listing in our
 
 
 
Our Web Page
STS Blue Logo
Check us out!
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.  
VFD'S for Centrifugals?
 
 

Can you put a Variable Frequency Drive on a multi-stage centrifugal air or gas blower?  Absolutely!  Will it reduce your power costs?  Maybe.  Will it hurt the motor or blower operation?  Probably not.

 

Centrifugal blowers have been in service long before VFD's came on the market.  For the most part, they were all designed to operate directly driven at a speed of 3600 rpm.   Each blower is designed for a specific  volume and pressure.  Changing the performance was accomplished by changing the impeller configuration.  In some instances, the blowers' performance was improved by belt driving it to a higher speed, but not much more than 4000 rpm.

     

Positive displacement blowers on the other hand, are usually belt driven, and their performance is changed by varying the speed(interchanging the sheaves).  VFD's revolutionized the PD blower market by making it so easy to vary the blower performance with the turn of a dial on the variable frequency drive.     

 

Log CurveControlling the centrifugal blowers with VFD's is like day and night compared to PD's.  Their performance changes with the speed, but in a much different way. As the speed of the centrifugal decreases, the pressure capabilities are decreased by the square!  The attached logarithmic curve shows the steep loss of pressure in relation to speed.  A minor speed adjustment of 100-200 rpm could reduce the blower pressure to less than your system pressure resulting in no air!  

 

VFD'sIf a blower system is operating at its' design performance, then the motor is most likely operating at peak efficiency.  Lowering the speed slightly would result in only minimum $$ savings.  VFD's help better if your actual system pressure is much less than design.  The lower you can decrease the speed, the more savings in power costs. 

 

From a maintenance point of view, the speed of the blower has no effect. Although there are still some motors out there that are not suited for VFD control, the majority of motors on centrifugal blowers can be operated safely with VFD's.  Installing a VFD is generally just a matter of replacing the motor starter.  If you are considering the switch, contact us for competitive pricing, and assistance with calculating your ROI.      


© Copyright  2010 Snyder Technical Services, LLC.  All Rights Reserved


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: 
 
What is the Balance Piston?
Thought for Today:
    "Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming--Wow!--What a ride!"
                                    -- Erma Bombeck
 
                          
methan gas extraction sytems logo