a pump includes a housing that contains a liquid , and a rotor including a plurality of blades extending radially from a shaft , and defining a conical space . a port member is disposed within the conical space . the port member defines an inlet port in communication with a low pressure region , a discharge port in communication with a high pressure region , and an anti - cavitation port in communication with a fluid supply having a pressure between the low and the high pressure regions . each pair of adjacent blades cooperates with the liquid and the port member to enclose a variable volume bucket , wherein rotation of the rotor selectively positions a bucket in an inlet position adjacent the inlet port to draw in fluid , in an anti - cavitation position wherein the bucket is adjacent the anti - cavitation port and fluid is admitted into the bucket , and a discharge position wherein the bucket is positioned adjacent the discharge port to discharge fluid .