Cross phase in radial directions with sensors ninety degree apart is 150 degrees

This is coast down peak and phase data. It shows amplitudes dropping and then at lower speeds it goes up again. I read in Vibration Institute course book that this signature indicates bent shaft.

I broke my neck looking at your photo

My apologies Becar

When your bump test shows 30 Hz NF, than definitely you are dealing with resonance.

I agree with you Becar. There is a sister pump in same pit with same N/F but it’s amplitudes are half of this pump.

I always say each machine has its own dynamic characteristics. It is quite often that two identical machines act differently. One can be more resonance prone than the other one. The cause is often in the surroundings; base plate, supporting construction, bad welding etc...  However, from your runup graph I cannot see any high vibration levels at 3,3 mm/s. You can give some more details about the machine and about your acceptance criteria.

Hi Becar,

Thanks for taking time to help me. I agree with everything you said. The coast down data is from test that was conducted with low water level in the pit. When water level in the pit is high, vibration amplitudes go beyond HI specification limit of 0.13 in/a RMS

You should provide more details:

- motor power

- photo of the machine

- where does your limit value come from

- phase curve if possible, I can only see amplitude curve

etc...

the vibration is still low, but if you have observed a change in the trend this could probably be a slack in the centering devices or the shaft

Thanks guys, I think I know what’s going on. I will present my conclusions later.

If 1X changes due to water level only, consider the effect of added mass to the entire pump system. This may explain a change in Fn.  Hard to know for sure without a more complete ODS.....

Have you considered a bump test for Fn at several different water levels?

Regards

Jim P

With high water level in the pit, natural frequency does not change.  Vertical looseness goes away with high water level. it reduces damping and amplification factor increases. This explains why vibration amplitudes amplify with high water level in the pit.

I will return to site in coming weeks. I will share more information later.