PURPOSE: To facilitate pressure control, by setting the flow rate of a final-stage impeller smaller than that of another impeller and by causing the final-stage impeller to perform work only in a range of small discharge.
CONSTITUTION: When the discharge quantity of a pump as a whole is large, the energy of a fluid given by an impeller 3 is so small that the total lift of the pump is almost determined by impellers 1a, 1b in upstream stages. When the discharge quantity of the pump as a whole is small, the ratio of the quantity of the fluid flowing through a return passage 4 and on a low-flow-rate impeller 2 is made so large that the total lift is augmented by a pressure increase caused by the low-flow-rate impeller 2, to facilitate pressure control.
YOSHIDA MASAO
YANAGISAWA SEIJI
NAKAE SHIGEKI
