Abstract: On the basis of the traditional formulae for the width of impeller and the specific-speed, the formulae of the increasing coefficients of the flow-rate, head and the specific-speed are deduced, which incarnates the relation between the increasing coefficients and the hydraulic parameter of the pump. The cal-culation method of the increasing coefficients for low specific speed centrifugal pump is proposed, based on performance prediction of centrifugal pump. The problem is resolved, which design condition efficiency for low specific speed centrifugal pump is not the highest in terms of experiential statistical in-creasing coefficients. The example indicates that the method proposed is practicable, which can enhance the efficiency of low-specific speed pump at design condition. The design theory of low specific-speed centrifugal pump is further enriched.

Key words: Design condition, Efficiency, Increasing coefficients, Low specific-speed centrifugal pump