We performed a experiments of a characteristics of a centrifugal pump with the open type impeller to clear the influence of the viscosity and the clearance against the performance of the pump. A clearance between a blade and a shroud, the viscosity of employed liquids are varied respectively in experments.
　We obtained the following results.
　(1) The performance of the pump can be expressed systematically by Reynolds number. In the characteristics of best effjcient point, a ratio of decrease of total head and discharge and a ratio of increase of shaft power are smaller than that of the closed type impeller as the viscosity of the liquids increases.
　(2) When the clearance is short, a characteristics of b.e.p. of the pump diminish linearly against the ratio of the clearance. Their diminishing coefficient depend on Reynolds number. In region of Re≦104, the coefficient of total head and efficiency increase and that of shaft power decreases. And their coefficient are constant in region of Re＞104.