Use of audible sound for safe operation of kinetic pumps

Abstract

Safe operation of kinetic pumps, as liquid movers, can be threatened by cavitation phenomenon, among others. Cavitation is the Achilles heel of kinetic pumps. It can deteriorate hydraulic performance, damage the pump by pitting and material erosion, and structure vibration and resulting noise. Cavitation can appear within the entire range of operating conditions; therefore it must, by all means, be prevented. To prevent cavitation in a pump, we have to know the beginning and development of cavitation in the pump. For this purpose, the emitted noise in the audible range can be used, among other possibilities. Experiments have shown that there is a discrete frequency tone within the audible noise spectra, which is in strong correlation with the development of the cavitation process in the pump, and so with the net positive suction head ( NPSH) critical value, which corresponds to the 3% drop in the total delivery head. The discrete frequency tone can thus be used to detect the incipient of cavitation and its development as well as to prevent the onset of the cavitation process in the pump and also in situ operation. Two different measurement methods were used to clarify the noise-generating mechanism, which is responsible for the discrete frequency component: by using a microphone and an accelerometer. Experiments have shown that the characteristic discrete frequency tone, which is in close correlation with the cavitation process, is a result of structural vibrations (modes) or resonances caused by implosion of bubbles and bombardment of the inner surfaces of the pump.