Abnormal Vertical Pump Suction Recirculation Problems Due to Pump-System Interaction

Paper No. 91

Abnormal Vertical Pump Suction Recirculation Problems Due to Pump-System Interaction
By D.R. Smith, S.M. Price, Bruno Schiavello
Proceedings of the 21st International Pump Users Symposium
March 2004

It is well documented that the proper operation of vertical centrifugal pumps is greatly dependent upon the entire pump/piping system, which includes the piping geometry and the system operating conditions. Oftentimes, pumps operate satisfactorily during shop tests but experience problems after they are installed in the field. Here, three large vertical pumps that operated satisfactorily on the test stand experienced excessive vibration after installation. Additionally, pulsation in the system piping was found to be causing unexpected vibration in downstream equipment. It was discovered that the problems were the result of complex interaction between several phenomena. Improper inlet conditions caused suction recirculation which generated broadband turbulence. The turbulent energy excited acoustical resonances of the pump/piping system, resulting in pulsation at several discrete frequencies. This energy subsequently excited mechanical natural frequencies of the motor/pump/piping system causing high amplitude non-synchronous vibration of the pump and other structures far downstream from the pump. Field data are presented. Diagnostic techniques and instrumentation needed to obtain the field data required to solve these problems are discussed. Also, additional data from pump hydraulic analysis and sump model tests are presented. Further, the solution strategy with two-step field changes (sump and pump) is shown. Following these modifications, the pumps have operated satisfactorily for more than four years.

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