Excess hotwell pump vibration

[terminator4]

I have a hotwell pump that is giving me fits. It has been operating great and running within acceptable limits for years. It runs around .13 ips vibration which is pretty much identical to the other 2 pumps. Around the 1st of summer it jumped up to .4 ips while the other 2 remained constant. We uncoupled the pump from the motor to determine where the vibration might be coming from. The motor has acceptable vibration. When we were recoupling we noticed that the tolerance on the coupling was set too close. It was readjusted and the vibration came down to .25 ips. The pump is in a vertical arrangement. Does anyone else know what might have caused the jump, and how do we get it back down to acceptable limits (.2 ips or less)?

Thanks

 

[Hatch]

You don't mention the frequency(s) of the high vibration, which can provide a significant clue to your problem. However, I have seen the follwing items cause high to severe vibration:

1) Pump shaft runout.

2) Motor overload due to motor damage or pump impeller wear, or a system change (they don't always tell you that there has been a process change).

3) Pump natural frequency has changed because attachment stiffness has changed. Check the anchor bolts between the steel base plate and the concrete foundation. Then check the bolts between the pump and the baseplate. You could loosen one or two slightly to see if there are any changes.

4) Some vertical pumps use bushings in the coupling between the motor and pump. A worn bushing can cause severe vibration.

I have worked on a hot well with 3 "identical" pumps. One pump always runs about twice as high as the others. We have never been able to determine why. All the parameters (above) were checked out and are roughly the same as the other two. We reduced the vibration of the rough pump by adding structural bracing to the motor. This reduced the vibration to a level the same as the other two.



Hope that helps.

 

[terminator4]

Thanks that helps some. I will look at what you mentioned. The frequency first occurs at start up at 70% of running speed. At that speed the frequency is 1251 CPM, at running speed (1800RPM) the frequency is approx 1800CPM and that is where the .25ips comes in. We changed the lift setting on the motor pump from 1/32 inch to 3/16 inch and had the reduction.



Thanks

 

[rob768]

Is it possible that pollution of the impeller causes unbalance vibrations?
Are one or more bearings worn, causing loss of support of that particular bearing position, thus increasing unsupported shaft length and introducing lateral vibrations.