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JuddJones

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Reply with quote  #1 
I was very pleased with the discussion on reading time waveforms. I learned a great deal, and received some great links to information, so I thought I would try it with another topic that I am pondering. How do you handle reading piston style pressure compensated hydraulic pumps? It was suggested on a similar thread (that I started) on "another" forum to look for bearing defects in the pump while ignoring the majority of the other "noise" created by the pistons and the rotating assembly. I can't help but think that there has to be a better way to handle it, but I have seen new perfectly good pumps with readings as high as .6-.8in/sec on the piston pass frequency. The same pump reading the next month will only read.15 in/sec at the same frequency. Also, how are you supposed to get a repeatable reading on a pump that is pressure compensated for flow? I could see reading the pump at 0 flow to check the condition of the bearings, but what about the compensater and piston assembly? How can that measurement be taken with any kind of reputability (or can it)? The only idea I could come up with was to force the pump over the relief to take a reading with the pump at full stroke, but that is a lot of work (and heat) to take monthly readings. The attached file is an example of a reading on a HPU that shows the piston pass frequency with harmonics.

Thanks for taking the time!

 
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doc Planer_HPU.doc (68.50 KB, 36 views)

Noknroll

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Reply with quote  #2 
It would be difficult to have same conditions on each survey, I guess you could note flow and pressure, higher/lower than previous survey as a guide to what you will expect to see amplitude wise. You could look for side banding around vane/piston frequency as an indicator for wear. Keep a lookout for cavitation also. You could also take oil samples
Edwin

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Reply with quote  #3 
Indeed, overall velocity or acceleration is useless in this case. I have also such equipment to monitor. All the bullets are yellow or red in the hierarchy. (i.e. overall alarms)
The thing to look for is developement in other spectral components: sidebands, noise and non-harmonic components.

But then again, if you find such developement and signs of damage, it still is hard to determine the severity of it. My experience is that those pumps are very strong and robust and almost never break down. An operator will stop it before it breaks down because he gets afraid of the noise [wink]

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Big Al

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Reply with quote  #4 
I have found piston pass harmonics to be always present, but variable (within limits) in amplitude. Typically I'm looking for any new frequencies outside of these. The couple of times that I've seen piston pass frequency really take off have both been caused by a blocked filter.
RBT

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Reply with quote  #5 
The best way I have found to monitor these pumps is by pressure, which is probably an operator function as they collect the readings from their walk arounds. Just this week we had to change a pump because the pressure started dropping. Also, the pump will start leaking much oil because of the violence of this pump the seals give way. When the pressure starts to drop the shoes and swash plate is starting to wear.
MarkL

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Reply with quote  #6 
If your worried about background noise, maybe setting a envelope alarm or band alarm may help? I suspect like roots blowers the background noise is the same, (I always find them a pain in the butt to monitor)
If you can access pressure readings I would say add it as a manual input on your analyzer, I have pressure readings on all the hydraulic pumps I monitor, I always take the pressure after the vib readings that way I can correlate any difference in trend etc.
Not sure what gear you use, but I am sure there is scope to add a manual input point and set the units to bar/psi etc?
kawanabadi

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Reply with quote  #7 
i have recently hydraulic pump damage.  The team already take vibration data a week before the day of accident.

Theses guys are fail to prevent recognize early failure may exist.

By this available data, should it say something or we have to adjust line resolution in order to catch the failure before getting worse.?

Thank you,
Iwan

 
Attached Files
pdf vibration_prior_to_breakdown.pdf (151.30 KB, 46 views)

Danny Harvey

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Reply with quote  #8 
Iwan,

Welcome to the forum.

It would be better and less confusing if you would move this post to its own topic.

It will save others the time required to figure out that it has nothing to do with the original post.

Thanks
Ralph Stewart

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Reply with quote  #9 
Quote:
kawanabadi

6 hours ago i have recently hydraulic pump damage.  The team already take vibration data a week before the day of accident.

Theses guys are fail to prevent recognize early failure may exist.

By this available data, should it say something or we have to adjust line resolution in order to catch the failure before getting worse.?

Thank you,
Iwan


The data pictures are, at least for me, difficult to read clearly. [smile]

Your first question "By this available data, should it say something"

I am not sure how the analysis is performed, but it should say something.


Your second question: "we have to adjust line resolution in order to catch the failure before getting worse.?".

It looks like you could use more resolution in the data.


Back to the way the analysis is performed...........

(1) Do they analyze strictly on trend values or do they look at most every waveform and spectrum?

(2) In the data your are showing, why or how is the set mark on the 7500 cpm peak and its sidebands chosen? By the software or by the analyst?

(3) Is the 7500 cpm peak really 8.33x or is it 8x?

(4) Why are the sideband markers measuring such low amplitude peaks rather than the larger ones left and right of the set mark point?

(5) Is it possibly that the larger peaks are running speed sidebands off the 7500 cpm peak or actual 1x running speed harmonic peaks, or something else's harmonics?

(6) Most of the peaks between 0 and 15000 cpms appear to be modulated by something, in addition to, either being harmonics of possibly running speed, and/or also themselves modulating something. This is where the more resolution would be good, to determine what is riding on these frequencies.


Thanks and Have a Great Day,
Ralph

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kawanabadi

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Reply with quote  #10 
Dear Danny Harvey,  Thank you for your advice.


Due to more focusing and prevent distracted with original topic, i had make new topic on this link;

http://www.machineryanalysis.org/post/printadd?forum=473361

Dear Ralph Steward, i had post better resolution on that link [smile]

respond for your comment will submitted on new topic.

many thanks for your respond.

Regards,
Iwan


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