Pump Vibration
Pump Vibration
(OP)
We have a pump with an ~25' shaft running at variable speed up to 229 RPM and power up to about 450 Hp. It had some initial high vibration but after two years of operation it is now vibrating to the point of tripping. Extensive vibration and modal analysis has been done and the conclusion is a bent shaft. Is it possible that the cause is imbalance on the impeller? I'm trying to get a handle on how a bent shaft would get progressively worse. Any insight would be appreciated.





RE: Pump Vibration
RE: Pump Vibration
Is the 229 rpm a typo? What is the service? As far as explaining how a bent shaft gets progressively worse, would you expect it to get better?
RE: Pump Vibration
I picture the pump being constructed something like this -
http://www.gouldspumps.com/getattachment/Products/...
So you are actually measuring vibration on the motor which is about all that is above ground, like this -
http://www.rainbird.com/images/products/ag/pumps/V...
Do you have more detailed information about frequency and even phase of the predominant vibration?
Is it 1X the pump rpm, or some other frequency?
Have any resonance tests been made on the pump. looking for the first bending mode / "reed" frequency?
RE: Pump Vibration
If my guesses are correct, then you should look at your bearings, in particular the bottom bearing (sometimes called a sand bearing). It is not at all unusual for a pump like this to experience crippling vibration with a small bit of imbalance. Typically (just guessing) you have a large weighted, high diameter impeller/propeller hanging on a shaft; once it starts to get unbalanced, things go awry quickly. If one of the lineshaft bearings gets worn, it will also degrade quickly.
Give us a little more information: Make, model, flow, head, shaft diameter, bearing arrangement, open/closed lineshaft. These details should be available in the pump's file folder, if you can find it.
RE: Pump Vibration
Johnny Pellin