Small pump with constant failures 4

[NovaStark]

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.

 

[electricpete]

it may be unlikely that the rotor becomes unbalanced every single time

Perhaps the pumped solution plates onto the impeller or corrodes impeller. Just a thought.

look at plots attached and see if they can determine anything additional that I can do to solve the problem.

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?

=====================================
(2B)+(2B)' ?

 

[Compositepro]

This pump has failed numerous times and the only information you have is vibration spectra? How about opening your eyes (or someone else's) and and examining a failed pump?

 

[NovaStark]

This pump has failed numerous times and the only information you have is vibration spectra? How about opening your eyes (or someone else's) and and examining a failed pump?

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.

Perhaps the pumped solution plates onto the impeller or corrodes impeller. Just a thought.

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.

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?

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.

 

[Compositepro]

A glass/vinyl ester impeller would be prone to errosion or cavitation damage. I would expect that bleach solution would have a fair amount of dissolved gas, which would promote cavitation. But this is simply speculation until the pump is examined.

 

[NovaStark]

Well there is a degassing tank which provides suction to the pump however its internal condition to see how well it is functioning is unknown.

 

[BrianE22]

Check alignment of pump shaft to motor shaft.

 

[NovaStark]

Check alignment of pump shaft to motor shaft.

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.

 

[Tmoose]

How long did the original brand new from the OEM pump last?

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.

 

[NovaStark]

When you said "a new pump is installed" are you referring to a rebuilt/ "overhauled" pump as a "new" pump ?

Yes sorry, this is correct. Not a new pump from an OEM a rebuilt pump.

When you "remove the pump for overhaul" what parts are replaced?

Usually just bearings and if needed, a seal.

I will have to check to see how well they can actually align the machine.

 

[MikeHalloran]

You need to study the OEM's rebuild instructions, then,

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

 

[drawoh]

Check alignment of pump shaft to motor shaft.

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.

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

 

[CouplingGuru]

This would be a great case study for us. I see you are using a Woods Sureflex on a 3.5" BE. Because you don't have space to align, the ability to measure flex element gaps and aligning off of that would be a great option for you. If you don't get a solution, give us a call, this would be a great case study. At 3500 rpm, that will eat elements left and right if there is any misalignment. If it works good to start then goes back, I would tend to lean toward a coupling/alignment problem.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM