Patent ID: 7766613

Claim:
A pump comprising: a pump unit including at least two impellers for sucking and discharging a liquid, the impellers being disposed in multiple stages; a pump case accommodating the pump unit and provided with a suction port and a discharge port for the liquid; a motor unit for driving the pump unit; a plurality of guide blades forming plural guide paths in tangent directions of the impellers; and a multiplicity of return blades radially disposed between the impellers to form paths for collecting the liquid under pressure from the guide paths into a suction opening of a next-stage impeller, wherein the return blades have a configuration in which a total cross sectional area of inlet openings of concave paths formed by a plurality of ribs is set to be equal to or larger than a cross sectional area of the suction port, while a total volume of the concave paths is set to be smaller than the total volume of non-path portions excluding the paths.