We have a three impeller horizontal centrifugal BFW pump driven by motor through gear coupling. The pump was commissioned in 1992. Since than this pump is having problem of high vibrations. Particularly in vertical. Amplitude remains in the range of 70 to 100 and velocity from 9 to 15. Trial had been done as suggested by many experts but there was no improvement. Line tension, balancing, bearings, Lubrication etc. are the critaria tried. Please suggest if any thing can be done.

I suggest to check the vibration of the gear coupling and impeller individually. First running the machineto check the vibration at the bearing with the shaft without impeller and then with the impeller.
If you can identify where the vibration is you can easily balance it with help of the vibrometer.

quote:

Originally posted by mkota:
We have a three impeller horizontal centrifugal BFW pump driven by motor through gear coupling. The pump was commissioned in 1992. Since than this pump is having problem of high vibrations. Particularly in vertical. Amplitude remains in the range of 70 to 100 and velocity from 9 to 15. Trial had been done as suggested by many experts but there was no improvement. Line tension, balancing, bearings, Lubrication etc. are the critaria tried. Please suggest if any thing can be done.

You please check coasting down of the pump. There you will get resonance frequency if at all. You can try with this solution
Increase rigidity of the base frame by regrouting or more rigid base frame of the pump.
Inthe coasting down spctrum at certain frequency vibration level will increase just like anything & at that time there will be 180 degree phase change.
If possible you can reduce the bearing distance span by modifying journal of the shaft.

hope it will help you. If any further clarification required send mail roytk@sify.com

Tarun

Being the vibration is in the veritcal direction, a resonance or natural frequency is very possible. If you monitor a coast-down, make sure the vibration makes the change Tarun stated or just drops away quickly.
Natural Frequency = square root of k/m (stiffness/mass).

If the vibration frequency is below the resonance frequency then stiffen. If the vibration is above the natural frequency then add mass. Be careful not to do both unexpectedly.

I can explain further if needed. lforeman@mac-reliability.com

Dear Mkota
I think you should check alignment and rotor run out.
regards
Anis

What frequency is the high vibration signal? Running speed? 3X running speed? Vane pass? Etc...

If you are assuming the vibration is at 1X using an "overall" vibration reading that could explain the difficulty you are experiencing in diagnosing the root cause.