PURPOSE: To obtain a torque flow pump which will never cause overload from zero head to no-discharge head by setting the ratio of suction port/diameter/volute chamber height/outlet diameter, output angle of impeller, the ratio of inner diameter/outer diameter of impeller chamber.

CONSTITUTION: In this torque flow pump, the flow path diameter variation rate of torque flow pump having volute casing is set to 100:85W51:100W150 while the output angle of impeller is set to 15W35° and the ratio of impeller chamber inner diameter/impeller chamber outer diameter is set to 100:90W60. When setting the dimension at each section of pump with such ratio, the end of shaft power curve can be made horizontal and saturated with high pump efficiency without requiring additional system in pump structure resulting in widening of operating range of torque flow pump.