Pumps & Systems - September 2007

which few people talk about. I have seen the significant effect it has on mechanical responses.

I agree with your 12 facts and suggest that if testing be conducted on the effects of misalignment it should also include the various coupling designs to be conclusive. By the way, after several years the elastomer design began to fail due to elastomer deterioration and the fact it took what I called a torsional set that affected coupling balance. We standardized on the disc pack design about 1988, and it is used to this day at that refinery.

Mike Polk

Lev Nelik replies:

Good to hear from you, Mike! Now we are talking! We are finally getting facts, not preaching. Clearly, your experience of trying to apply a different coupling, without changing alignment, shows that people have valid reasons (which we should respect before judging too quickly) to do so, not simply because they are lazy or do not care.

In fact, I found (and was personally involved, so I know the facts in this particular case) similar issues with a gear type coupling; it failed in one year due to severe misalignment. When we inspected it, the coupling teeth were worn out severely on one side in a pattern showing gross offset misalignment and signs of axial movement as well, i.e. angularity issues. When we followed up, we found out the folks at the plant did not do any alignment at all – and did not know they were supposed to. Had they used a different coupling, as you suggest, they might have gotten a longer time before failure, but even then it would probably not be a pretty picture.

Again, the main reason for failure in their case was not aligning to 0.002-in, but simply knowing the difference between pump alignment and planting toma-toes. We helped them understand what they needed to do in the future. They appreciated that and the fact that we tried to help them, instead of making them feel like idiots or sending them to the library to get a degree in couplings.

I have learned over 29 years in this business that when someone does not know as much as I do in one thing, they often know a lot more than me in many other areas, so I try to hold on judging them and try to appreciate the position they are in.

Again, good to hear from you, and thanks for your feedback. Stay in touch.

I greatly enjoyed Lev Nelik’s article “Revisiting Pump to Motor Alignment” (Pumping Prescriptions, July 2007). I’ve been kicking tires and slamming doors on pumps for 50 years now (tried retiring, but they came after me with dogs and guns), and I’m very skeptical of many of the claimed reasons for improved MTBF.

Let’s look at where the average user was in 1957 vs. 2007:

1957 2007

Cementatious Epoxy

Lubricated Gear Dry Disc Straightedge or RDI Laser

What’s That? 11,000 max.

Sized for Stability Sized for Reliability Flood Mist

Unrestricted Restricted

Rare Common

2 years but who cares? 10 years and we work at it

Grout Couplings Alignment Suction Specific Speed Minimum Flow Oil Lubrication Pump Design (Note ¹) Vibration Monitoring High MTBF

Note 1: In 1957 we pretty much accepted whatever the pump manufacturer recommended for the service. Today, the user takes a more active role. That has driven some

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