Studies on the Vortex Pump : 4th Report, Cavitation Characteristics

For the purpose of improving the suction performance of the vortex pump, a study was carried out on cavitating in a vortex pump with a standard type impeller. The cavitation was classified into four according to the region of occurrnce. The cavity in each region occurred at vortex centers along a discontinuous velocity surface, where a very low pressure allowed the inception of cavitation even at high NPSH. As NPSH was decreased, the pump head and efficiency gradually decreased in the partial discharge range ; however, they showed an increase with the shaft power, at a certain NPSH in the over-discharge range. This rise in pump performance was due to an increase in blade work because the cavity caused the flow on the blade suction side to thrust toward the pressure side. An improved impeller, based on this observation, was suggested and its superior suction performance was confirmed.