On the run misalignment adjustment

[plawrence]

Can you safely place shims under motor feet on the run by loosening one foot at a time?

Patrick

 

[dgallagher]

Definately not a safe endeavor. Plus, how do you know your making the proper correction if you haven't done an alignment check first? Could make matters worse, cause machine damage or personal injury. Take the time to shut down and do a proper check and correction. Be safe.

 

[plawrence]

So here's the rest of the story:

We're experiencing high 1X vibration on an overhung pump (Ahlstrom ERS-30, 14x12, 1800 rpm). Last week one of our PM guys noticed a bad shake and sure enough, it had jumped from 0.23 to 0.95 ips. We shut the system down, pulled the runner and found nothing in the bowl or wedged in the impeller. However, we did see the impression of a bolt left in the impeller. That seemed to be a very likely cause of the imbalance (had our annual outage about a month ago--could have been a left over part) so we put everything back together, aligned it as best we could (I'll get back to that) and after about an hour it was running at about 0.3 ips. Checked the next day, still the highest reading (always pump inboard horizontal) was about 0.3. Hooray.

Until the same thing happened yesterday--running fine and then jumped up to 1.9. We shut it down, pulled the runner--no damage--put it back together and aligned it. Gets up to temp and runs from 0.75 to 0.83 ips with 99% of the energy at 1x and a little bit at 6x (vane pass).

So, how can I get rid of this 1x vibration problem? The pump horizontals are about 4x the pump verticals and about 10x the motor horizontals.

What I know so far:

The pump bowl was changed last year. The guys that put it in said it bolted together perfectly--no pipe strain, at least when it's cold. But we did find a loose suction piping support leg this morning. Once we drove some wedges under its base, the overall dropped from 0.83 to 0.77. . . . It's a start.

I still need to get some more phase numbers that I'll put in a jpg and post in a bit.

So back to aligning this thing. We've always debated over where to leave the motor for thermal growth of the system. If the system is stone cold, we have great data on where to leave it and don't have a misalignment issue once we get back to temp (the process is controlled to 295°F). But, when we get into a situation like last week, where the pump and motor are continuously cooling down, we do some calculating and scratch our heads and leave it to where we think it will grow back and be OK.

Any help on this would be greatly appreciated.

Patrick

 

[Ralph2]

Not too sure I would want to loosen and raise a foot enought to add shims on a running application. You would likely induce some major vibration in the process.
But, I have "judicially" loosened one foot at a time in an attempt to find a soft foot that is causing vibration.
This is not a process to be taken lightly and without due consideration of the possible consequences.
Ralph

 

[jmack]

Just as a sideline. Check where this pump is operating in comparison to the best efficiency point. More than once I have seen overhung centrifugal pumps showing high 1 X because they were operating well off the BEP. If you are operating significantly (I hate these subjective adjectives) off the BEP for the pump you may be bending the shaft (high radial loading) and also loading the free bearing (usually NDE), not allowing for thermal growth. This can give you the 1X you have encountered. I have also had a great deal of success in dynamic balancing these type of pumps as a complete assembly (balance across the coupling), and have seen results where overalls were reduced by half. Good Luck!!

MacK