Timely detection of the occurrence of cavitation in pumps is very important as it can cause pitting, erosion, and loss of pump performance. Attempts to determine a unique signature of cavitation using vibration, acoustic emission, audible-acoustics, and higher order non-linear modeling techniques have been elusive. This paper presents the results of an experimental study undertaken first to understand the structure of cavitation and develop an effective means for detection of it. Tests were performed at SpectraQuest facility in Richmond, VA. using a fully instrumented test stand on a small centrifugal pump. We measured vibration, pressure, audible sound, motor current and the force due to cavitation of a centrifugal pump. A special force transducer capable of measuring fluctuating forces exerted by cavitation process on the pump casing was developed to understand the dynamics of cavitation phenomenon and signatures of a centrifugal pump operating under different cavitation conditions. Two of the abnormal operating conditions studied were the formation of tiny air bubble (initiation of cavitation) and then fully developed cavitation. Experiments were also run with a transparent LEXAN cover using colored water to observe the cavitation. A Video was also taken for observing and developing an understanding of cavitation mechanism. Vibration, force, audible sound, and dynamic pressure were analyzed to detect cavitation.
It was found that the pump has higher vibration amplitude in the axial direction than in the radial direction. This may be due to lower stiffness in the axial direction. From the experiments, it was also determined that significant amount of air bubbles will increase vibration component associated with the impeller vane pass frequency. Cavitation seems to excite high frequency structural resonances. Also, a fully developed cavitation may reduce the impeller vane pass frequency vibration amplitude. The force spectra did not provide any measurable information of cavitation. In addition, real world case studies will be provided. Presentation will also provide basic physics of cavitation; its damaging effect if not detected in a timely manner and step that can be taken to minimized it occurrence.
Dr. Suri Ganeriwala is the founder and President of SpectraQuest Inc. Suri has over 30 years of industrial and academic experience in machinery vibration diagnostics and control, signal processing and viscoelastic materials characterisation. Suri has worked for Philip Morris, Firestone and Martin Marietta Aerospace. He has developed a unique method of instruction using the SpectraQuest machinery fault simulator (MFS), which is his creation from concept to completion. He has authored over 50 papers and articles in journals, magazines, conference proceedings and books. He obtained a PhD in Mechanical Engineering from the University of Texas, Austin, USA. Suri serves on the MFPT Board of Directors and is Leader of the Signal Analysis Forum.