The machine is vertical CW pump. The NDE motor Brg is sleeve and the DE bearing is antifriction. Motor speed is 373rpm (8 poles)

The highest amplitude is 0.68X at motor DE radial (H and V), about 150 micron p-p.

Pls advice

150 micron pp- is that casing vibration, or shaft vibration?

Hello Steve

Vibration taken from the casing

Could you post a spectra for this machine?. As far as i can guess the .68X could be related to a lubrication problem (oil lash).

Ahmad,
Assuming no harmonics of 0.68x are present, my guess, it is a resonance. Bump it to prove or rule out. FTF is less likely as it is normally around 0.4x with harmonics and of small magnitude. Also, FTF has not manifested itself in other ways, which it should've if this was the problem.

If data is taken with a regular accelerometer beaware that vibration is probably understated due to roll off in accelerometer response curve(373x0.68=253cpm =4hz).

Also it is better to use velocity units to avoid double integration.

David

This message has been edited. Last edited by: David_G,

What is the DE side bearing number with make? We can find fundamental train frequency which is sub synchronous if it is a bearing problem.

Ops, I didn't notice that the measurement was taken on the antifriction bearing.

Anyway, i stand by what i said earlier. A spectrum graph of the machine would help a lot. It would be great also to know the number of bearing you have.

quote:

far as i can guess the .68X could be related to a lubrication problem (oil lash).

mechanical pawn, can you clarify what you mean by your content within the quote.

John from PA

I'll bet "whip" translates into "lash" somewhere

Dave

Ahmad,
How come your readings are taken from casing and your data is in microns? Is it taken from a remote accelerometer sensor or a handheld accelerometer?

wow, what a coincidence, i also have the same problem with our CW pump. The sub synch were about 2/3x and the radial. The pump has 6 blade. The vibration were taken on the casing using low freq accelerometer with 16 average.

spectrums.doc (52 Kb, 30 downloads)

I had similar case on the vertical pump running at 1200 rpm. I did the bump test and it was natural frequency of the motor and motor stand but it sounded terrible and we recommended to pull the pump .After it was disassembled we found the bottom bushing was missing and the impeller was bouncing inside the bowl. I suspect the impact was generating a wide range of frequencies and one was inducing the natural frequency of the motor/stand system.