The double suction volute pump consists of three components: a double suction flow path in upstream, an impeller with five blades, and a double volute flow path in downstream. The double suction was designed to improve a flow on the inlet surface of impeller. A significantly high pre-swirl velocity and low pre-swirl velocity were observed in original double suction, however its high pre-swirl velocity was slowed down and its low pre-swirl velocity was speeded up in designed double suction. As a result, the designed double suction had a more uniform velocity distribution on the inlet surface of impeller. The impeller had twenty design parameters and those parameters were optimized by genetic algorithm(GA) to improve the impeller efficiency. A high total pressure loss was observed on the outlet surface of impeller and near the shroud wall of impeller meridian surface. On the other hand, its total pressure loss was decreased in optimized impeller, and the impeller efficiency increased by +0.7[%]. The cross-sectional surfaces, which were defined on a main streamwise curve of double volute, were designed to decrease a total pressure loss occurring inside double volute. In designed double volute, a secondary vortex on the cross-sectional surface was suppressed and a high circumferential velocity was decreased near the tongue and front edge of partition wall. As a result, the total pressure loss was decreased inside designed double volute. The hydraulic pump performance for designed pump, which consisted of the designed double suction, optimized impeller and designed double volute, was predicted by numerical simulation. Efficiencies in double suction, impeller and double volute were increased by 0.6[%], 0.4[%] and 1.1[%] respectively and the total improvement of pump efficiency was 1.9[%]. The designed pump was manufactured and its hydraulic performance was measured by experiment. The numerical results of pump efficiency agreed well with experimental ones. The efficiency of designed pump increased by 2.0[%] compared with that of original pump in experiment.
