Detection of Cavitation in Centrifugal Pumps

Pumps are designed and manufactured to operate well away from the cavitation condition and thus the factors affecting the onset of cavitation are important. A specially designed test rig was and constructed so that the onset of cavitation could be studied visually while obtaining actual NPSH data. The magnitude of the NPSH level at 3% drop in total discharge head of a pump was determined at different operating conditions. Photographs were obtained with a high speed camera indicated that the state of cavitation existed long before the pump performance was affected, and well before the 3% drop in total discharge head criterion was applied. Correlations between the calculated NPSH at the visual sighting of the onset of cavitation and NPSH values corresponding to a 3% drop in total discharge head were predicted at various operating conditions. Flow visualization as expected revealed that the intensity of cavitation varied according to the operating conditions (flow rate ratio, pump rotational speed, and water temperature).