July 13, 2017
Pipe Strain Was the Issue
By Brad Case
Have you ever struggled with a precision shaft alignment, even though you did everything right? (Preformed the pre-alignment steps, controlled backlash, etc., etc.) So, what was different? Maybe it was pipe strain.
An alignment check of a new installation of a 40 HP, 3600 RPM motor/pump revealed the vertical angular misalignment was 3.2 times the tolerance of 0.5mils/1”, with the vertical offset almost 7 times the tolerance of 2.0 mils. The horizontal misalignment was better but also out of tolerance.
Several Verti-Zontal compound moves where made and though the vertical alignment was coming in it still wasn’t quite right (offset out just a few mils) and it seemed “overly touchy” to just a few thousand’s shim change at the motor feet. In other words, the motor wasn’t responding as expected when the shim changes were made.
The motor was also slightly bolt bound at the rear feet. The mechanics couldn’t get the horizontal angle below 0.6mils/1”. The decision was made to use the EVO’s Feet Lock function and move the pump horizontally to correct the bolt bound condition.
As the pump hold down bolts where loosened the pump sprang up vertically due to pipe strain, however the pump sprang up at a slight angle as it took 25 mils of shims under both pump rear feet, 50 mils under the right front pump foot and 20 mils under the left front pump foot to relieve the vertical pipe strain.
The Feet Lock Function provided a workable solution for eliminating the bolt bound condition without creating pipe strain horizontally. After tightening ALL hold down bolts a fresh set of measurements indicated the vertical offset was now 45 mils low at the coupling. This was expected as the pump was now higher. The vertical angle was out slightly.
Two quick Verti-Zontal moves and the alignment was finished with the coupling values well within the 3600 RPM tolerance (almost zero). After the pipe strain was relieved the motor responded as expected when adjusted.
Did pipe strain cause our alignment struggles? Absolutely. In this instance, it was well worth the 15 – 20 minutes it took to relieve it.
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