I need your suggestion,
I have a case and need your advise. I have centrifugal pump 2975 rpm, 520 kW. In april 2017, i have a dominant spectrum in 1x and 3x, 1x = 0.673 mm/s, 3x = 1.162 mm/s. But suddenly when I throttled the valve on 10% opened, the spectrum becomes 1x = 0.334 and 3x = 5.116 mm/s. Found harmonic 1x motor speed.
Firstly I thought that is the effect from cavitation. But i didn't see any raised floor on high frequency.