Test and analysis of abnormal vibration of vertical mixedflow pump
(1. School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei 430072, China； 2. School of Mechanical and Electrical Engineering, Nanchang Institute of Technology, Nanchang, Jiangxi 330099, China)
Abstract：To identify the reasons for the abnormal vibration in a vertical mixedflow pump, the vertical and horizontal vibrations were measured at the low bracket, pump lid and outside column of pump unit by using lowfrequency vibration sensors in startup and normal operation periods, the pump shaft run out were monitored by means of an eddy current sensor as well. The experimental data were processed by the Hilbert-Huang transform (HHT), and the vibration peakpeak displacements were acquired, and the eigenvectors of vibration signals were extracted to diagnose the type of fault; finally, the timefrequency feature in startup period was analyzed in order to search the root reasons for the abnormal vibration. The analyzed results showed that the vibration frequency of the pump unit was close to the unit rotational frequency in the normal operation; additionally, for the shaft orbit is similar to an eccentric ellipse, the type of fault in the unit was unlikely the rotor imbalance. During the starting period, the shaft orbit was chaos and the vibration amplitude was as large as 47.3 times the amplitude in the normal operation, suggesting a violent force might be generated in the starting period and eventually induces the rotor to operate in imbalance. The timefrequency characteristics of vibration signals in a pump can be acquired accurately with the HHT, especially for highly nonlinear signals; meanwhile, this study on vibration generated in a pump during its startup period will provide a new way for pump troubleshooting.
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