Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

Vibration and Noise in Pumps 485
Figure 18-40. Pump shaft vibration orbits.
times as long. A cascade plot of the vibration data (Figure 18-41) showed
that just before trip of the unit at 21,960 rpm, an instability vibration
component occurred near 15,000 cpm. From this and other data, it was
determined that the high vibrations were caused by:
• A sudden increase in nonsynchronous vibration as the unit approached
full speed resulting in shaft bow.
« A sudden increase in unbalance due to the shaft bow and as a result, a
rapid increase in synchronous vibration levels as the nonsynchronous
components disappeared.
After the problem source was identified using the above data analysis
technique, computer simulation of the rotor led to a solution consisting of
bearing modifications. The stability analysis of the pump rotor predicted
that the pump had an unstable mode at 15,000 cpm with a negative loga-