One point, a there is a force that is not usually accounted for in either laser or dial methods. The torque produced by a driver will cause relative movement between itself and the driven component. The torque that a motor applies to a pump will cause it to deflect or "roll" in respect to the base. Likewise the hydraulic forces applied to the pumpage will cause the pump body to "roll" the opposite direction. Even though the shafts may be perfectly aligned while at rest, and even if there is no thermal growth, the shafts will be dynamically misaligned. The amount of this misalignment is probably small in most cases, depending on the structural stiffness of the system components, and the actual torque applied.

This torque induced misalignment may not show up in vibration data if the torque is steady, but if the load pulsates it may be easily discerned. Nevertheless, the bearings still see the load and will fail prematurely.

Just want to make the point that this discussion on Alignment between myself and Mr. Pietrowski has been edited. It has been edited in such a way that some of my arguments have been changed and some have been omitted. Furthermore, Mr. Pietrowski's points have been embelished from our original discussion and there have been several additions after the fact. My views have not been properly represented in this posted discussion.

When you see this type of biased editing published in a forum without the input of one of the original contributors, you have to ask yourself why this would be done. I certainly have my opinion regarding the motivation to do something like this, I will leave it to others to reach their own conclusions.

My parting comment would be to warn people out there that just because someone writes a book or several books, it does not mean that the content of these books are accurate. Don't believe everything you read.

quote:

Don't believe everything you read.

Yea, but stuff on the internet is beyond reproach.

I hope everyone appreciates the point made. Evaluate the data for one's self.

Why don't you present your side here?

Brian, you will get a fair hearing here. We are a pretty independent thinking bunch... heck, we don't even agree with ourselves at times. This would be a good place to set the record straight.

Hi Brian,

Please accept my and Jeff Shuler's (Editor in Chief - Uptime Magazine) apology if you were not given a chance to see and approve the final version of the document that was supposed to represent the exchange between you and John.

We were both under the impression that you have been supplied the summary document that represented the discussion we posted here and that you have supplied permission to publish per Johns request.

Neither Jeff or I have any interest in having you or your words misrepresented here. Our interest in publishing this exchange was simply to allow the rest of us learn from what we viewed as a great exchange between two very intelligent people - who also happened to disagree. We also wanted to forum members to be able to add to the discussion - which is why it is posted here.

If you feel you have been misrepresented - please supply me with the accurate account (also copy John P as he did for you).

I do appreciate that you have already invested massive time into this project - but to set the record straight - would be most appreciated by Jeff and I as well as all the other forum members who are following this thread and learning a great deal.

I would also like to ask straight out: Did John supply you with the text that was posted here and did you state that we could publish it? We will still correct the record in either case or if you wish - we will delete this entire thread.

Thanks

Terry O

Brian,

Somewhere in the discussion (can't find it now) you said that misalignment can be detected from a TWF. Can you elaborate more on that?

Thanks,
David

Terry,

I read the Uptime article by J. Piotrowski. My understanding is that the scope of work was to measure shaft alignment movement from cold to hot operating temperature and to evaluate what effect shaft misalignment may have on the bearing and coupling failures. I have used both the tooling ball with inside micrometer method and the Dodd-Bar method that is similar to the Ball-Rod-Tubing apparatus, so I have familiarity with the methods and degree of difficulty.
A significant point of the paper was the measurement of substantial axial movement of the bearing housings that was attributed to casing thermal elongation. I have not used the pyramid (3-dimensional) geometry necessary to get axial movement, so I was curious if this was really a significant issue. I assumed a mircometer bar length of 24", zero horizontal and vertical movement, and 50 mils (0.05") axial movement using a right angle triangle. I calculated a change in apparent length of the bar to be 0.00005" (24.00005 – 24.00000). I hope my Trig math was correct! I cannot understand how the 50 mil axial movement (if real) would affect the accuracy of the horizontal and vertical movement measurements. My conclusion is that 3-dimensional measurement with inside micrometer method is not needed, and 2-dimension measurements are adequate for normal hot alignment measurement. The paper did not draw any conclusion on whether the axial movement of the bearing housings, and not the shaft ends, would affect coupling or bearing faults.

Walt

Walt

Thanks for the question.

We have asked John P to provide an answer which either he or I will post as soon as it arrives.

Thanks

Terry O