Reality of Cavitation Inception in Centrifugal Pumps

Pumps were designed and manufactured to operate far from the cavitation condition. Pump designer has defined the cavitation inception point as the point where the head drops by 3 %. This definition is incorrect, because the first appearance of vapour bubbles was observed earlier than 3 % drop in the head. Therefore using 3 % drop in head, as indication parameter for cavitation inception has always resulted in damage in pumps during operation. This paper describes visual studies conducted to determine the variation of net positive suction head with flow rate, rotational speed and water temperature. A special correlation between the visual net positive suction head and net positive suction head corresponding to 3%drop in head was predicted at various operating conditions.