BACKGROUND: A customer had called us in to take a look at a Liebert Cooling Fan. The fan was vibration excessively and had been for a few weeks. It was a small center hung fan belt driven by a 2hp motor.
FINDINGS: Spectral Vibration data was collected and analyzed on-site. We also collected the speeds of all rotating elements.
- The Motor 1750 RPM
- The Fan 1520 RPM
- The Belt 576 RPM
The data revealed a high axial vibration at 2 times the running speed of the belt. This is a sign of belt misalignment. Further investigation showed that the motor had an adjustable sheave that was not running true.
SOLUTION: We suggested that the motor pulley be replaced with a fixed type sheave, the belts be inspected and replaced as needed and that the belts be properly aligned.
After the repairs the unit was retested. The data showed that the problem had been eliminated.
CONCLUSION: In this case, the use of spectral vibration analysis quickly and precisely identified the fault. The practice of replacing parts and trying different things until the problem goes away, was avoided. This new approach save time and money.
