Does your pump have an alignment problem? Part 2
by Jim Elsey
April 24, 2019

Just because you have a vertical pump and motor with a machined motor support stand does not mean the alignment process can be skipped. I have witnessed several issues with mis-machined motor supports through the years. Never assume and always verify.

On vertical pumps with rigid couplings, I have found that something as simple as the bolt tightening sequence can alter the runout of the coupling alignment. I recommend a dial indicator on the coupling during the bolt tightening sequence to prove your work.

On horizontal pumps with either C- or D-face motor adaptors, the inherent alignment is not perfect because of manufacturing process tolerances. Depending on how the tolerances stack, you could be 0.007 to 0.015 inches off.

Last of all, and my favorite: “A pump is the most expensive pipe support you could ever purchase.” Do not use the pump as a pipe support.

Don’t be surprised when your pump has problems due to misalignment.

The more critical the pump, and the faster it operates, the more important it is to align the driver. A standard vibration test will tell the true story. It is not the pump’s fault if you do not do the alignment.

19 Tips & Common Alignment Mistakes

1. Safety first. Make sure the equipment is locked out and tagged out before you start. You are ultimately responsible for your own safety.

2. Do not waste time and money conducting an alignment on a unit that is already a piece of junk. If the foundation, base and supports are junk, then your alignment will be junk.

3. Before you start the alignment process, check the driver for soft foot first. Check one foot at a time while the others remain bolted. Know that there can be parallel soft foot and angular soft foot. Both types will drive you crazy if you do not know you have the issue. Angular soft foot is also sometimes referred to as “skew.” There can also be the phenomenon of “base soft foot,” where nothing is wrong with the driver foot, but the base has the issue.

4. Except in rare cases, always conduct the alignment with the coupling spacer removed or at the very least with the bolts loose or mostly removed. Realize and understand that you are really doing a shaft alignment, not a coupling alignment.

5. I recommend to match mark the coupling halves so they align and reassemble together. I also recommend that the keyways/key seats for the two shafts be placed at 180 degrees from each other. If the keys, keyways and key seats are all identical, it probably does not matter. They are not identical most of the time, and so this practice will help with balance issues.

6. Rotate both shafts together and in the same direction that they rotate in the operation.

7. Check for the proper distance between shafts prior to starting the alignment and watch for axial play that will corrupt the readings and, consequentially, the alignment.

8. Do not beat on the driver feet with sledge hammers.

9. Normally, you would never move the pump during the alignment process and always move the driver. But if the pump is a new installation and has not been piped in yet, it is acceptable to move the pump. A common mistake is to pipe the pump in before the first alignment is complete.

10. When using dial indicators, be aware of spanner bar sag, and know how to check and compensate for sag. Do not start the alignment without checking for sag.

11. Depending on what technique or equipment type you choose to conduct the alignment, be sure to check both shafts for runout. Should you encounter more than 0.002 inches runout on either shaft, you will likely have other problems. So, correct the runout issue first.

12. Dial indicator shaft buttons must be perpendicular to the surface they are touching.

13. Make sure the dial indicator button is actually touching the surface to be measured and that the travel length is not compromised. This is a common trick played on new personnel.

14. Do not expect a four-decimal place accuracy from a three-decimal place dial indicator.

15. Measure your shims. Just because it is stamped 0.010 inches does not mean that is the true size. In a game where 0.002 inches is the maximum tolerance allowed, understand that 0.001 inches can make a big difference. Keep shims clean and free of burrs and imperfections.

16. Never use more than four shims total (aka stack) per equipment foot and try to keep it to three or less. The more shims, the more spring and margin for error. Do not be afraid of machining custom shims to accomplish this goal.

17. Always use the same number and size of shims in both front feet and the same number and size in the rear feet. The front stack does not need to match the back and vice versa. Do not use a different number of shims (stack size) from side to side in an effort to roll the unit.