Acoustic and vibration diagnosis of cavitation for centrifugal pumps of different materials

Abstract

Cavitation has destructive effects on pumps. It causes mechanical damage, decreases discharge and efficiency, and increases noise and vibration. Therefore, it must be detected during pumping operations to find a way to eliminate it. This study concentrates on the effect of the impeller blades material of a centrifugal pump on cavitation and its impact on vibration and acoustic emission levels. Using an in-house pump system, number of experiments were performed on a centrifugal pumping system using three different impeller materials; stainless steel, brass and plastic. Cavitation could be detected by vibration and acoustic spectrum analysis. When cavitation commences, the flow conditions change and the noise and vibration of the pump increase. Since vibrations and noise are transmitted from the pump through its housing, the signal is not uniformly distorted due to the loss of transmission and the structure of the housing. Noise and vibration are steadily increasing, but the signal is more pronounced in certain frequency ranges than in other parts of the spectrum. The experimental results show that the plastic impeller gives the lowest level of sound and vibration compared to the stainless and brass materials. It is also evident that the amplitudes of the high frequency range of the sound spectrum are affected by the impeller material during normal operation of the pump. Cavitation results in further increase in the sound amplitudes in the high frequency range.