April 10, 2013
The Shaft Alignment Nightmare
By Stan Riddle
Sometimes precision laser shaft alignment is a quick, neat, orderly maintenance task. And sometimes, it is not! Occasionally, everything that can be wrong IS wrong.
While teaching a Fixturlaser Go Pro training class in Illinois, the class went into the plant for some “hands on” shaft alignment work. The machine chosen was a 25 HP motor coupled to an overhung centrifugal pump. This pump was chosen because it had experienced numerous coupling, bearing, and seal failures. And so it began.
During a quick pre-alignment inspection, these problems were found:
- The pump front support foot was broken at one of the bolt locations.
- The pipe support was loose, and not supporting the weight of the discharge line.
- The flexible joint connector on the suction side of the pump was misaligned.
- The shafts had been running about 3/8” out of alignment in the horizontal plane. That’s 374 mils of offset misalignment or about 93 times the 4.0 mils maximum allowable offset misalignment for 1800 RPM!
So, they went to work.
- The mechanics adjusted the discharge pipe hanger.
- Re-positioned the pump to alleviate the pipe strain on the suction flange.
- The motor base riser was cut loose with a grinder.
- A spare pump front support foot was not available, so it was decided that the foot would be useable as it was.
- The riser and base were ground smooth, and all mounting surfaces were cleaned with a brush to remove dirt and paint.
- The riser (with the motor still bolted to it) was repositioned, and tack welded into place. A rough alignment was done with a straightedge. The mechanics noticed that the motor was sitting too high, so the pump was shimmed a little vertically on the inboard feet.
- The riser was welded into place, positioned by using the GO Pro.
- The final precision shaft alignment was completed.
The next day, the maintenance managers commented that the pump had never run so smoothly. But there was one problem. The new oil seal was leaking, because it had been running in such a misaligned condition.
So, the moral of the story is? Just about everything that could be wrong, from a shaft alignment standpoint was wrong. But, through a little patience, persistence, and using some common sense, all these problems were repaired in a couple of hours. And replacing the oil seal would alleviate the remaining problem.
great post…thanks for sharing
Step back, assess the situation, roll up your sleeves and get to work. Great on the job training!