Abstract:

The vibration instability during the startup process of mixed flow pump seriously threatens the safety of the pump unit, and through the research of the orbit of shaft centerline, it can comprehensively and visually reflect the transient effect on the stability of unit operation and hold the vibration state of rotor under abnormal operation condition . Based on the Bentley 408 data acquisition system, it obtained the rotor axis locus chart and time domain chart during starting process under different rotational speed, and purified its the rotor axis locus chart and time domain chart of the 1X and 2X frequency , and analyzed the spectrum diagram under different rotating speed .The research results show that, during the startup process , the orbit of shaft centerline chart of the 1X frequency is from a ellipse which long axis and short axis is similar gradually into a circle, and it can judge that the rotor has arcuate rotating vortex and the vortex is increasing; the orbit of shaft centerline chart of the 2X frequency is from similiar horizontal line segment gradually into a horizontal flat ellipse, and it can judge that the rotor has eccentric phenomena and the horizontal vibration is increasing. Connect to the transient external characteristic curve, the study found that as the speed increases gradually, and the rotor system transient hydraulic load increases gradually, and the rotor imbalance and radial offset increases gradually, and the vibration situation gradually aggravate, when the speed reach maximum, a peak is coming in shafting vibration and with the speed tends to stability it decreases and gradually becomes stabilized. Acceleration is the main cause of shafting vibration, and transient effects are the important factors influencing the deterioration of vibration. The research results for the real time assessment of shaft system operation state during the startup process of mixed flow pump, and for reducing or preventing the deterioration of vibration effectively has important value of engineering application and theory instruction function.

Key words: orbit of shaft centerline, starting period, vibration, mixed-flow pump