July 6, 2011
Cooling Tower Adventures
By Brad Case
The OJT portion of a recent XA alignment training class led us to a two-cell cooling tower that had a run of bad luck–motor bearing failures, internal supports broken, visibly shook when it ran, etc.
A cursory visual inspection revealed no shims under the 25 HP motor and a horizontal gap difference of ~3/8″ between the gearbox hub to the spacer shaft. That 3/8″ gap over the 8″ coupling works out to 47 mils/in of angular misalignment! No wonder it was falling apart!
The motor/spacer/gearbox were ‘roughed in’ pretty quick using the handy line lasers and 30 mm detectors on the XA sensors. The XA was setup to take readings in Tripoint mode and a first set of results were obtained. The vertical results showed the motor to be too high by ~75 mils. Remember–there were no shims under the motor. So now we’re base-bound. No problem. The FeetLock™ function was activated and the optimal move was calculated. A tiny 10 mils under the front feet of the gearbox and 45 mils under the front feet of the motor was all it took. Since the motor was also bolt-bound, FeetLock™ was used again to find the optimal move. After re-measuring, a slight additional horizontal correction was made and then re-measured one last time to verify the results.
An hour and 45 minutes is all it took to rough it in and align it within spec for it’s operating speed. After start-up the shake was gone and the customer was smiling.