What a Way to Blow up a Blower!

Most residential and commercial HVAC equipment use centrifugal blowers to move air through duct systems.  The rate at which blower wheels turn is usually between 1000 and 1500 rev/min, depending on the application.  The point to be made is that blower wheels turn at a fairly slow speed.  Blower wheels that are attached directly to the motors that drive them turn at the rotational speed of the motor.  But, when the blower wheel is belt driven, the speed of the blower can vary depending on the size of the pulley attached to the shaft that drives the blower wheel.  If the size of the pulley attached to the blower shaft is twice as large as the pulley attached to the motor, the speed of the blower will be half of the speed of the motor.  If however, the blower pulley is the same size as the motor pulley, the blower will turn at approximately the same speed as the motor.  If the blower wheel is not designed for such speed, the centrifugal forces created by the rotational motion will cause the blower wheel to fail in a spectacular way.  The photos attached below illustrate the results.   

Blower louvers peeled away from blower ring
Blower louvers peeled away from blower ring
View of damage to blower louvers

About R.J. Hill, P.E.
R. J. Hill is the author of two blogs: R.J. Hill Consulting and the Descendants of James Alexander Hill. Mr. Hill is a registered professional (mechanical) engineer with over 39 years of experience, 34 years in private practice. Please visit www.rjhill.com to see the kinds of forensic investigations that Mr. Hill performs.

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