Sidebands of pump rotation harmonics
Sidebands of pump rotation harmonics
(OP)
Measuring vibrations on a multistage pump (water pump) I find strong sidebands around rotation harmonics
Rotation is close to 3000 rpm (50 Hz) and side bands about +/- 2.5 Hz
Pressure fluctuations in the fluid are impossible
Any idea about the possible causes of such a phenomenon?
Thanks and regards
luimont
Rotation is close to 3000 rpm (50 Hz) and side bands about +/- 2.5 Hz
Pressure fluctuations in the fluid are impossible
Any idea about the possible causes of such a phenomenon?
Thanks and regards
luimont





RE: Sidebands of pump rotation harmonics
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RE: Sidebands of pump rotation harmonics
I find sidebands on the pump bearings
Motor shows normal spectra
Theoretically a transmission through the baseframe can occur but what I see is not just an increase,it is a creation of sidebands
luimont
RE: Sidebands of pump rotation harmonics
2nd guess as you have appeared to rule out is fluctuation related to the fluid system... valve or load changing at 2.5hz.
If you rule out the above you have definitely ruled out all the likely candidates. The only other things I can even take a wild guess would be oscillation in the power system (possibly including vfd if present) that might cause torque oscillation at 150cpm.
And if I brainstorm what might possbily oscillate at 2.5hz to cause sidebanding I can guess resonance of very very flimsy structure (spring mounted machine or extremely flimsy cantilever support). Actually I did have spring mounted machine that had the spring resonant frequency (200cpm) as sidebands to 1x. It didn't fit any of the charts but I postulated possibly as the machine slowly wobbled on it's base it was changing unbalance or misalignment response (even though both motor and fan were on same base). Also possibly torsional resonance of flexible coupling... never seen it but seems possible.
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RE: Sidebands of pump rotation harmonics