Solution of Cavitation Problems in Pumps by Means of Model Air Testing

This paper describes a case of rather unusual and severe cavitation in a double-suction centrifugal pump and the way the problem was corrected. The cavitation was demonstrated in a heavy erosion in the impeller blades while the performance of the pump did not show any signs of deterioration. The original design of the pump and the operating conditions were rather conventional with the available NPSH exceeding the recommended Hydraulic Institute Standard values. To solve this problem it was necessary to study, in detail, the velocity pattern at the impeller inlet. For this purpose, a wooden model of the pump suction nozzle was built and tested with air. A three-dimensional picture of the flow distribution in the impeller eye was obtained from this test indicating a considerable nonunlformlty in both the circumferential and the radial direction. This information led to the redesign of the impeller-inlet passage which ultimately eliminated the cavitation.