Thread: Balancing a fan
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Don Foreman Don Foreman is offline
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Default Balancing a fan

On Fri, 14 May 2010 10:02:20 -0500, "Pete C."
wrote:


Karl Townsend wrote:

I got so much help on my sprayer, I'm trying again...

Full time investigation and part replacement has me working on this theory
of the problem cause: The squirrel cage fan is out of balance. It is barely
detectable because the fan has a 2" solid steel shaft and some serious
pillow block bearings mounted solid to a beefy frame. At the resonate RPM,
this imbalance feeds on the slack in the drive line. Any system upset causes
the fan to become unstable and it lurches back and forth.

I've called around and not found a place to dynamic balance something like
this. Are there any home brew methods? Or other suggestions? Its built so
solid I don't think I'm looking for a minor imbalance.

Karl


Remember that any vibration would relate to the rotational speed of the
item out of balance. Can you get your hands on a resonant reed
tachometer? The RRTs are recommended for isolating vehicle driveline
vibrations by identifying the frequency of the vibration so you can
correlate it to which driveline components rotate at that frequency.

As for fan balance, if you just take the drive belts off you should be
able to turn the fan by hand to identify any issues. Mark the fan and
spin it by hand a few times and see if it is stopping near the same
orientation each time.
Again, I doubt it's the fan since I expect it's spinning a lot faster
than the 540 RPM PTO and won't have a 9 Hz period if it has an
imbalance.


I agree. I also don't see how fan imbalance would generate torque
ripple. I would suspect some aspect of the drive line between PTO and
gearbox: pulley, bent shaft, any couplings or U-joints, etc