Impeller Eye Shift - Vibration Trouble 1

[nationalpump]

Ladies and Gents,

We are investigating the cause of vibration during the operation of a cantilever pump. It should be noted that the pump has vibrated ever since the impeller was changed some months ago.

We have found that the center of the impeller eye is NOT the center of the impeller vanes. We have measured the varience and have determined that the center of the impeller (the white dot in the photograph) is 0.25" off from the center of the impeller vanes. My question is whether or not this would contribute dramatically to a hydraulic imbalance or if this varience should be no problem at all. The impeller is 13.87" in diameter. The rotational speed is 1200RPM. The cantilever shaft is ~4 ft. long from the lower bearing.

Please note that the dimensions given in the attached picture are 3" from the center of the vanes. The white dot is the actual center of the impeller and also coincides with the position of the shaft (it is centered on the back of the impeller). Again, the varience is 0.25" from impeller center to vane tip center.

Our belief is that the impeller vanes are unevenly loaded causing the measured vibration. I look forward to your thoughts.

Thanks in advance.

Adam

 

[nationalpump]

Please note that we have balanced the impeller and reinstalled it with no change in vibration. The impeller has also been ground true to the 13.87" diameter.

Adam

 

[nationalpump]

It is worth mentioning that the pump is operating appropriately on the pump curve.

Adam

 

[Artisi]

If the impeller eye centre is "not in the centre" ie, the blades are displaced off-centre when it is a good bet it is hydraulicly unbalanced.

 

[Strong]

I would not suspect hydraulic unbalance. I would test for natural frequency that can amplify vibration levels.

Walt

 

[786392]

I believe
After any works on impellers dynamic balancing is a must to avoid problems subsequently since we have most affected/ sensitive member of the system at risk; in a way!

Best Regards
Qalander(Chem)

 

[nationalpump]

The impeller was dynamically balanced & installed. Post balancing the vibration remained. Any other thoughts or experiences?

Thanks all.

Adam

 

[786392]

Probably Normally on a shaft mounted condition at the most usually experienced RPM's?

If the above is correct and true.
May I suggest to check its balance in a pan like manner with respect to It's Center of gravity and recheck through dynamic balancing then repeat till fully balance either way?

This is just out of blue,I suggest;for possible trouble shoot indeed.

Best of luck

Best Regards
Qalander(Chem)

 

[nationalpump]

We balanced the impeller at operating speed. I guess I am not clear on what you are refering to when you suggest checking the balance in a "pan like manner". Are you suggesting static balancing? Thanks!

Adam

 

[786392]

Just Visuallize the

Impeller removed from shaft and Very very Critically statically balanced for its center of gravity in a Nice horizontal flat condition,therafter rechecked for dynamic balancing and few times rechecking/repeating the process.
Slight trial and error to resolve the issue I mean.

Best Regards
Qalander(Chem)