Yes? No? Maybe? Yes!
You may have heard this in the past…”We can’t align our vertical pumps since there is no adjustment due the ‘machined fit’ between the electric motor and pump housing. Plus it has a rigid coupling!”
You may want to rethink this one.
The OJT portion of a recent training class involved a large vertical Floway pump driven by an 800 HP GE electric motor, rotating at 1200 RPM, utilizing a rigid coupling with a piloted fit.
Since we didn’t want the coupling and shaft stiffness to influence the alignment readings, the decision was made to remove the coupling bolts and rest the impeller in the pump bowl, treating the pump as a non-rotating shaft. The other option was to loosen the coupling bolts just enough for an approximate 0.050″ gap between the coupling hubs which would still allow pump shaft rotation but would have eliminated the coupling stiffness issue.
In this case the class wished to practice a non-rotating shaft alignment using the Fixturlaser thin magnetic brackets.
The sensors were mounted and alignment measurements were taken. The thin magnetic bracket with the S sensor on the pump shaft was moved to each measurement location, then the motor shaft with the M sensor was rotated to the same position before the measurement was registered. Note: When using the Vertical Alignment program in the XA, a bolt in the motor mounting circle is labeled #1. The alignment measurements are then registered with the sensors first pointed at the #1 bolt, second at 90 deg. and third 180 deg. from the #1 bolt.
For 1200 rpm, the allowable angular misalignment is +/-1.0 mil/1” with an allowable offset of +/-6.0 mils at the coupling center. The initial alignment results revealed the offset misalignment (as viewed from 90 deg. to the #1 bolt) was out of tolerance. The other coupling values were within tolerance.
The four motor hold down bolts were loosened with the XA monitoring the moves in real-time and the motor was pushed from right to left (as viewed from 90 deg. to the #1 bolt) to correct the out of tolerance offset misalignment. Yes–there was clearance in the “machined fit”. The motor hold down bolts were tightened and a fresh set of alignment measurements were taken and the results analyzed.
All coupling values were now in tolerance. 46 minutes from “As Found” to “Final”!
9 Comments
[…] Mount the sensors across the coupling. Special considerations might need to be made for rigid couplings or with space considerations. (http://thealignmentblog.com/blog/2011/09/15/vertical-pumps-alignment/) […]
I have a problem of vertical pump shaft suspected misalignment because the ratial alignment is 0.03 mm
high vibration observed in pump motor non drive end.
what is your comments
what moderation
What is the RPM of the motor and pump? You mentioned the radial misalingment is 0.03 mm, what is the angular misalignment? If the angular misalignment is not in tolerance as well it can contribute to high vibration as well.
reply to me
What is the allowable axial and angular runout/misalignment between pump and motor shafts during erection and commissioning of VT pumps
Anmol, I would recommend checking with the speciffic pump manufacturer, or your engineering deprtment, for specific alignment tolerance recomendations.
@Brad Case, do you have a detail explanation of how the thing magnetic bracket is mounted in the non rotating shaft. A comment was made regarding a need for indexing it. What does that really mean and what is the purpose of doing it.
Luis, indexing refers to ensuring the thin magnetic fixture is seated properly on the shaft or coupling hub. There or two small “indexing” screws on the face of the thin magnetic fixture that need to sit against the outside diameter of the shaft or hub. I am unable to attach a photo in this reply so I will email it to you with red arrows pointing to the two screws.
Thanks for your comment.