Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Resonant Frequencies in Pump Operating Range - How Far to Stay Away
(OP)
Hello All,
I am interested in hearing resoning for the minimum range to stay away from resonant frequencies in a pump's operating range.
For some context, the pumps I am interested in are vertically mounted centrifugal pumps on the order of 900 HP, used to pump water (in a wastewater application). The pumps are having vibration issues on the motor non-drive end. I believe this is the "reed" frequency.
I have read some literature that says to stay at least 10% of full operating range away from known resonants. I have read some other lit that says 25%.
What is the industry standard?
Can anybody quote any standards (ISO, etc.)?
Any anecdotal evidence.
Thank you,
Chris
I am interested in hearing resoning for the minimum range to stay away from resonant frequencies in a pump's operating range.
For some context, the pumps I am interested in are vertically mounted centrifugal pumps on the order of 900 HP, used to pump water (in a wastewater application). The pumps are having vibration issues on the motor non-drive end. I believe this is the "reed" frequency.
I have read some literature that says to stay at least 10% of full operating range away from known resonants. I have read some other lit that says 25%.
What is the industry standard?
Can anybody quote any standards (ISO, etc.)?
Any anecdotal evidence.
Thank you,
Chris





RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
ISO13709:2009 (aka API 610-11th)
"Generally, a 20 % margin of separation should be maintained between
the natural frequency of the motor support structure and the operating speed."
You said operating RANGE, is it on a VFD? Can you avoid the vibration with a change in speed?
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Yes, it is on a VFD, and we can adjust speed. Right now, the speed varies according to inflow, and can sometimes trip out the pump on vibration.
The operators have a few work arounds, but as you surmised, we are trying to develop operational protocals to keep the pump away from its resonant frequencies (i.e. do not operate pump from 45-85%).
I forgot to mention, this is actually a group of 5 pumps that all work together.
Thanks again,
Chris
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
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RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
thread384-264106: Dynamic absorber presentation - for comment
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(2B)+(2B)' ?
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Did you confirm the resonant frequency (hit pumps with a mallet and record vibration spectrum) or do you just know that it sometimes trips at a given pump speed? Which could also mean it trips at a given inlet flowrate. Or it could mean that it trips on Sunday morning, the point being: keep a broad perspective while gathering information.
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Does it happpen on individual pumps or is it on multi-pump operation, does sump level change during operation etc etc.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
The pumps are all in a sump.
This problem happens when all the pumps are running.
I will keep an open mind, the research continues...
Thank you for all the help!
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Regards,
SNORGY.
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Once again it's was the pump/s at fault. Why is the first call always " there is something wrong with the pump/s" when a problem comes up - doesn't anyone ever consider that a lot of these pumps, designs and hydraulics have been round since Adam was a boy and run perfectly well under the conditions they were designed for and quiet often run well away from the design conditions.
I would wager a bet that if all the "something wrong with my pump/s" posted here were analysed, the majority would be other than pump problems.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
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(2B)+(2B)' ?
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
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(2B)+(2B)' ?
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Electricpete, Yes the problem vibration occurs when all pumps are running together. Yes, the problem vibration occurs under the same loading condition (i.e. at a certain total flow over all the pumps).
The work around has been to shut down one pump and run only 4 at a higher rate to avoid the "problem-zone" of operation.
I am trying to organize some run-up/run-up down tests (at varying flows), and will hopefully have some more info.
Thank you all for the comments, you have given me alot to consider.
Thanks,
Chris
RE: Resonant Frequencies in Pump Operating Range - How Far to Stay Away
Is it a sump or a forebay configuration, how are the pumps arranged - a sketch or some photo's might help throw a bit of light on the problem.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)