Sign up Calendar Latest Topics Donate
 
 
 


Reply
  Author   Comment  
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 471
Reply with quote  #1 
Most of our pump vibration standards for acceptance tests have overall limits as well as discrete frequency (or filtered or narrowband) limts. For example, the limit for a given pump would be 3 mm/s, but any given frequency/order (1x, BPF, etc.) cannot exceed 2 mm/s. In practice, a pump that is compliant with narrowband limits is compliant with the overall limit, and a pump that exceeds the overall limit also exceeds the narrowband limit. Therefore it seems a little redundant to have both criteria unless  we expect a lot of broadband noise contributing to the overall. If there is though, its something we will have to fix regardless.

I am familiar with 'power band' limits, but these are not absolute limits, they are trend-based limits.

Also, I see the use of having different limits for each 'fault band', but then why not have different values for different orders? For example, 1x should not exceed 1.8 mm/s, 2x should not exceed 0.6 mm/s, BPF should not exceed 2.5 mm/s, etc.

My company is trying to overturn the requirement for these narrowband limits. It will make life easier for them, but they do not have the physical argument to say its okay. I'm trying to make that physical argument, but its hard to do that if I can;t even understand why they were put in in the first place...

Any ideas?
George D

Member
Registered:
Posts: 35
Reply with quote  #2 
I don’t recall that any of the ISO family of vibration standards uses the filtered designation? They recommend a frequency range (eg up to at least 1000 Hz ). I would have to wade through my HI, API, NEMA. etc to confirm whether any others do? The GM standard has band alarms. Beyond that, my recollection is that the “filtered” term is used primarily in vendor specific thresholds?
I agree, it becomes onerous to separate all these different criteria? And doubtful, in my mind, whether it’s even useful? Maybe just recommend adopting one of the more generally accepted ISO standards?
Thanks for posting, look forward to hearing responses...
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 471
Reply with quote  #3 
George, ISO-10816 has these filtered limits in chapter 7 on pumps (bottom of table A.1), but not in most (all?) of the other chapters. In some cases, it says that 5.0 mm/s is okay, but both 1x and BPF must be below 2 mm/s, which is insane to me!

So you have both those frequencies at 1.9 mm/s, barely compliant, then your RMS overall is still just 2.7 mm/s. You would need quadruple the energy to exceed an overall limit of 5.0 mm/s. Where does that come from if not 1x or BPF?

API 610 is similar, but again, HI is generally the voice of reason IMHO:
"Measurement of vibration filtered to discrete frequencies is not applicable for acceptance testing of pumps according to this standard."
George D

Member
Registered:
Posts: 35
Reply with quote  #4 
Agree with everything you say. Vibration during an acceptance test, and within the preferred operating range, should be predominantly 1x and vane pass?
Thanks for pointing this out, I clearly read this section before because I have highlighted notes on my copy? Have no memory of it though? I’m gonna hide my own Easter eggs this year.
Seems like somebody on the standards committee may have had a special purpose or agenda here?
John from PA

Sr. Member
Registered:
Posts: 810
Reply with quote  #5 
Quote:
Originally Posted by Curran919
Most of our pump vibration standards for acceptance tests have overall limits as well as discrete frequency (or filtered or narrowband) limts. For example, the limit for a given pump would be 3 mm/s, but any given frequency/order (1x, BPF, etc.) cannot exceed 2 mm/s. In practice, a pump that is compliant with narrowband limits is compliant with the overall limit, and a pump that exceeds the overall limit also exceeds the narrowband limit. 


Maybe...see https://www.maintenance.org/topic/1x-vs-overall-amplitude
OLi

Sr. Member
Registered:
Posts: 1,494
Reply with quote  #6 
I did some work for a 1 blade pump producer way back and the "hydraulic unbalance" (that I never knew existed since I never saw a 1 bladed pump before.....) that it created could be compensated but the pressure transients tore pipes off the wall, just FYI.
__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,566
Reply with quote  #7 
Is “BPF” generally used for pumps? I would agree that 1x and vane pass would be the major concerns for a new pump, but there could be some harmonic content as well if there was any looseness in the bearings. Obviously there shouldn’t be on a new pump, but if the same standards are used for rebuilt pumps you’d want looseness covered because not all shops do good work all the time. I would also think that broadband noise has to be addressed, from the perspective of an owner who has someone else spec the pump (vendor, architect/engineer), because if it’s not a good fit for the system there could be substantial “noise” in the spectrum. Will overall limits catch broadband noise?
__________________
"The trend is your friend"
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 471
Reply with quote  #8 

Quote:
Originally Posted by OLi
I did some work for a 1 blade pump producer way back and the "hydraulic unbalance" (that I never knew existed since I never saw a 1 bladed pump before.....) that it created could be compensated but the pressure transients tore pipes off the wall, just FYI.


Hydraulic unbalance is highly important in pumps. I've also worked on 1-blade impellers that are used in waste water for their anticlogging nature (e.g. we specify 6" spherical objects to be able to pass through the pump). They are difficult to mechanically balance, but depending on your relative flow, the vector for the hydraulic unbalance is not only much higher than your residual mechanical unbalance, but it changes angles almost 120 degrees. I was part of a redesign to not necessarily decrease the magnitude of hydraulic unbalance, but to get the angle lower over the range of flow rates, so that it could be compensated with mechanical balancing. We were only able to get it down to 60 degrees, but that allowed some compensation.

Quote:
Originally Posted by Rusty
Is “BPF” generally used for pumps?


Yes, BladePF and VanePF (number of impeller blades) are essentially interchangeable. pressure pulsation relative to the number of diffuser vanes only exists in the rotating frame of reference, and is essentially never measured.

Overall limits would catch broadband signals. Discrete/Narrowband limits do not. Harmonic signals (such as from looseness) do not exist in new machines and API and ISO discrete limits are only used for acceptance tests.

Quote:
Originally Posted by John
Maybe...see https://www.maintenance.org/topic/1x-vs-overall-amplitude


I hope you aren't insinuating that my question is as basic as that one... Of course i know these fundamentals of vibration quantification... different amplitude formats (RMS/peak) and pseudo-true methods, RSSing overalls... everything in that thread. Should I post a link to my own course on the subject?

Otherwise, that thread has zero relevance to this one.

OLi

Sr. Member
Registered:
Posts: 1,494
Reply with quote  #9 

I just did straight field balancing exercise in the test-lab  test setup as that was what I was contracted for, to test if it was possible. Call was like "can you balance a pump? Standard answer, yes if it rotates and I can add weight.", not knowing what I would see and hardly believing what I saw when I saw it.... Impeller was balanced in balancing machine to compensate for 1 blade.
Brute 1 plane balancing worked like a charm and what went on after that I have no idea, just being a consultant. Reference from pipes falling off the wall was from a plant where all
indications pointed to such a device being used w/o taking care of the consequences.  


__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
electricpete

Sr. Member
Registered:
Posts: 517
Reply with quote  #10 

Quote:
Impeller was balanced in balancing machine to compensate for 1 blade.

Can you explain what you mean by that.
Did you mean to say "to compensate for 1 blade missing"?

OLi

Sr. Member
Registered:
Posts: 1,494
Reply with quote  #11 
Well if you make a impeller with 1 blade you have substantial weight to add to make it balanced in a form that in this case was a lump of iron and not in the shape of a blade.
When you start rotating it with media you find that a lump of the media do rotate with the single blade pump and mess up the "dry" balancing and requiring a significant new compensation for that by doing a "wet" balancing or whatever you may call it. I was quite surprised that it was possible but you always learn, every day. I was not prepared to meet this thingy either so, interesting.
Calling it missing is maybe misleading as it is made like that on purpose but my normal pumps have sort of symmetry and this on purpose are not symmetric and that make it interesting.

__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 471
Reply with quote  #12 
Pete,

Here is an article about one of our old single-blade hydraulic designs, including a picture of the impeller:

https://www.pumpindustry.com.au/pumps-engineered-for-extremes
ivibr8

Sr. Member
Registered:
Posts: 122
Reply with quote  #13 
Curran
Going back to your original question.....
The first versions of the software I used (Azima DLI Alert) allowed me to create narrow-band alarms for higher frequency problems (gear mesh & bearing defects) using acceleration units and overall levels with velocity units.

The usefulness of this approach can be debated (in fact, as their "Expert" software developed, these user-defined limits became obsolete) but I can tell you that there were instances where this seemed to be helpful. It also helped to have some knowledge your particular machine and its past history of symptoms and findings.

Regards
Jim P
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 471
Reply with quote  #14 
I feel a little better about my stance. Here is my reasoning:

I went through the old versions of the standards to see when this requirement for filtered limits came in. For API 610, it was 1981, when amplitude was still defined as 0-pk. When considering 0-pk signals, unfiltered data will be highly dependent on signal impulsivity, whereas impulsivity is completely removed for filtered values. DIfferent information is therefore contained in each quantity. On the other hand, unfiltered RMS values tend to reject impulsivity altogether, so what is really the difference between an unfiltered and filtered value? I think the filtered requirement is leftover from the 70s standards and doesn't really serve a purpose anymore.
MarkL

Avatar / Picture

Sr. Member
Registered:
Posts: 920
Reply with quote  #15 
Was it written on a leather bound tablet?
Sheesh that API stuff is Hilarious, talk about scared shirtless about change.
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.