Use of noise and vibration signal for detection and monitoring of cavitation in kinetic pumps

Abstract

Cavitation in kinetic pumps causes lowering performance, mechanical damage and increase of vibrations and noise. Therefore, it is important to detect inception and development of cavitation phenomenon in the pump. This paper deals with signals of vibrations and noise, which will be used for detection and monitoring of cavitation in kinetic pumps, and also to prevent the effect of cavitation in the pump and pumping system. When the cavitation is increasing, the flowing conditions are changing, which leads to an increase of vibrations of the pump and emitted noise in the surroundings. Because vibrations and noise are transferred from the pump through its casing, the signal is non-uniformly distorted due to transfer losses and structure of the casing surfaces. Even so, it is possible to determine development of cavitation phenomena from the measured signal. Noise and vibrations are increasing steadily, but in some specific frequency ranges the signal is more pronounced than in other part of the spectrum. Experimental results have shown that when the cavitation is fully developed, the measured signals at a characteristic frequency or range of frequencies start to decrease. This characteristic frequency or band of frequency is discussed in this paper, and also comparison between theoretical expectations and measurement results was performed.

Cavitation Detection in Variable Speed Pump by Analyzing the Acoustic and Vibration Spectrums

“…Cernetic et al [5] studied two centrifugal pumps; pump A made of metal alloy with 6 blades closed impeller. Pump B made of plastic material with 6 blades semi-open impeller.…”

Experimental analysis of cavitation in a centrifugal pump using acoustic emission, vibration measurements and flow visualization

“…The trend of the Welch estimator is similar with those presented in other works [12, 14 & 15] at the same frequency range, with the use of microphones. At the range of 0-3 kHz the amplitude differences are indiscernible due to the cavitation interaction with the low frequency mechanical noise caused mainly by the BPF and its harmonics [15]. However, at higher frequencies those harmonics become weaker and the broadband noise increases due to a more pronounced cavitation effect (Figure 8).…”

“…Similarly to [12], three different discrete tones were selected for each impeller and all of them appeared at a sharper increase than the total noise level curve. Cernetic et al [15] presented the variation of the total head and relative amplitude of vibrations with the NPSH for two different pumps, one with a metallic closed impeller and one with a plastic semi-open impeller. The vibration results for the two impellers are for different frequencies; the metallic impeller is for a frequency band around 1600 Hz and the plastic for the discrete frequency of 148 Hz.…”

“…The same was observed for the frequency band studied in relation to the geometrical characteristic of the impeller. For all the cases presented in [12][13][14][15][16], the maximum noise or vibration level coincided with a 3% total head drop.…”

Acoustic Detection of Cavitationinception

“…The main types of cavitation (partial attached cavities, travelling bubble cavitation, vortex cavitation and shear cavitation) were presented. Cernetic et al (2008) performed experimental work using signals of vibration and noise which used for detection and monitoring of cavitation in kinetic pumps. Their experimental results indicated that when cavitation is fully developed, the measured signals at a characteristics frequency or range of frequencies start decrease.…”