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Severe vibration on critical fan threatens medical research
Problem: Extremely high vibration on a 100 horsepower motor, driving an important exhaust fan at a medical research facility, was discovered to have a severe vibration condition. Analysis of the vibration spectrum pointed at a "soft-foot" condition. Soft-foot describes the condition where one or more of the 4 motor feet (like legs of a table) are not in the same plane. Just as a table with uneven feet will rock, the motor with this condition can vibrate greatly, and when the feet bolts are tightened, the motor frame distorts. The resulting uneven motor air gap contributes to the high vibration.
Correction: By using feeler gauges, and loosening the motor feet bolts, the amount of gap was determined by the MRG technician. Shims were fabricated to take up the space, and the motor feet were retightened.
Result: The overall machine vibration dropped from 1.5 ips (inches per second) to just 0.15 ips. Machines of this type should normally run less than 0.2 ips for long life. This motor was headed to a early grave, costing as much as $5000 for the replacement and repair. The costs of possible lost research and scientist productivity loss could have been significant. |
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| Related
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Fan motor; green arrows show where shims were installed
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Severe vibration before repair
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Smooth running machine with no "Soft-Foot"
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