Complete Characteristics and Suction Performance of Screw-Type Centrifugal Pump.

Complete characteristics of a screw-type centrifugal pump were obtained experimentally, and the performance of this pump as a reversible pump-turbine was estimated. Moreover, effects of a net positive suction head on pump characteristics were investigated. As a result, it was found that this pump has a good head-discharge curve and a good limit-load characteristic, and the pump efficiency is superior to that of conventional non clogging pumps. However, this pump is not suitable as a reversible pump-turbine, because the efficiency is inferior to the pump efficiency when it is operated as a turbine. We observe a phenomenon wherein the head and load suddenly increase just before the break-off point of pump efficiency with decrease of the available net positive suction head. Based on the result of flow visualization, it seems that this phenomenon is caused by an increase in the theoretical head due to the occurrence of cavitation in the impeller passage. The required net positive suction head of this pump is smaller than that of conventional centrifugal pumps, and it is found that the suction performance of this pump is superior to that of pumps with the same specific speed.