Small pump with constant failures
Small pump with constant failures
(OP)
Hi,
For the past few years I have had a pump that has now reached on a run until failure type status. It is used to pump NaOCl into sea water as treatment. Typically what happens is that a new pump is installed and after about a month or so, the vibration starts to increase until after about 6 months or less, noise starts getting louder and vibration reaches about 1-4 in/s. By that time, we have to remove the pump for overhaul. At that point all vibration points on the pump and motor are high (above 0.5 in/s).
Vibration spectra only show a dominant 1XRPM frequency and the waveform shows high impacts. Unfortunately that sole frequency does not really tell me much about what the problem is as it may be unlikely that the rotor becomes unbalanced every single time. I have suggested possible issues such as structural related problems but due to cost, I can't really provide much evidence based on my plots that I have.
Perhaps someone with more experience can look at plots attached and see if they can determine anything additional that I can do to solve the problem.
Note that '1' denotes motor NDE, 2 - motor DE, 3 - pump DE and 4 - pump NDE.
For the past few years I have had a pump that has now reached on a run until failure type status. It is used to pump NaOCl into sea water as treatment. Typically what happens is that a new pump is installed and after about a month or so, the vibration starts to increase until after about 6 months or less, noise starts getting louder and vibration reaches about 1-4 in/s. By that time, we have to remove the pump for overhaul. At that point all vibration points on the pump and motor are high (above 0.5 in/s).
Vibration spectra only show a dominant 1XRPM frequency and the waveform shows high impacts. Unfortunately that sole frequency does not really tell me much about what the problem is as it may be unlikely that the rotor becomes unbalanced every single time. I have suggested possible issues such as structural related problems but due to cost, I can't really provide much evidence based on my plots that I have.
Perhaps someone with more experience can look at plots attached and see if they can determine anything additional that I can do to solve the problem.
Note that '1' denotes motor NDE, 2 - motor DE, 3 - pump DE and 4 - pump NDE.
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RE: Small pump with constant failures
I didn't look at the plots, but it seems that a careful examination of the removed pump and motor would be the logical starting point in understanding these repetitive failures.
Is there any info available about the condition of the equipment after it gets removed?
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(2B)+(2B)' ?
RE: Small pump with constant failures
RE: Small pump with constant failures
Yes and now that I can actually dedicate my own time to see about it, that is what I will do. However I wanted to know if there is anything one more experience could tell from the plots. Otherwise what generally happens is that the pump will be removed, bearings and seals replaced and then reinstalled without my knowledge. Like I said, the pump has pretty much gone onto a run until failure status wherein if the vibration reaches 0.3 in/s and I request that the pump be removed for inspection, I will get a response to wait until the vibration reaches 1 instead.
Once the pump is removed I will check it out but the impeller is glass vinyl ester material which should be ok for the service.
None yet however there is a similar installation nearby which does not have the same time between failures which the only difference is the foundation and base plate.
RE: Small pump with constant failures
RE: Small pump with constant failures
RE: Small pump with constant failures
RE: Small pump with constant failures
The funny thing about this one, is that when I ask how they align the pump to motor, they say that can't fit the brackets to use reverse dial method so they use a straight edge.
Thus if I ask them to recheck alignment I get the response questioning if the spectra show misalignment and the coupling takes up any misalignment.
RE: Small pump with constant failures
When you said "a new pump is installed" are you referring to a rebuilt/ "overhauled" pump as a "new" pump ?
When you "remove the pump for overhaul" what parts are replaced?
I picture new bearings possibly are bearing installed, and the original worn shaft and housings are re-used and the fits are mighty loose.
Please don't post any detailed pictures showing the installation and coupling type, or the coupling make, model, and number.
If you check out other vibration analysis related bulletin boards, despite what the VA wall charts say, you may hear some folks don't hold much truck with even detailed vibration measurements reliably diagnosing shaft/coupling misalignment.
RE: Small pump with constant failures
Yes sorry, this is correct. Not a new pump from an OEM a rebuilt pump.
Usually just bearings and if needed, a seal.
I will have to check to see how well they can actually align the machine.
RE: Small pump with constant failures
YOU, PERSONALLY,
need to witness the complete sequence of such a rebuild as conducted by your crew.
Do not take notes or even carry a clipboard.
Do not comment or make suggestions or ask questions.
But do record what happened, as soon as possible, without talking to anyone in the interim.
Take particular note of the tools used, and how they are used.
Then, by yourself, compare your crew's process with what the OEM recommends.
... in writing.
Mike Halloran
Pembroke Pines, FL, USA
RE: Small pump with constant failures
Do you have access to this pump? If the problem were straightforward, they would have solved it themselves, without your help. As noted above, you need to take apart and examine everything yourself.
--
JHG
RE: Small pump with constant failures
When it comes to couplings we are always here to help.
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