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The series experimental schemes were designed, including five different heights from the bell-like open to the top, four distances between the backwall and the vertical axial center, three backwall types of rectangle, semicircle and symmetric volute, and with no diffuse bell-like pipe in tank-style outlet passage. By testing, hydraulic loss was got and flow patterns were observed. Based on analyzing test data, the varying law was obtained between hydraulic loss and five different heights with different Fourier numbers. The suggestions were put forward that the height from the bell-like open to the top must be higher than 0.36D0 and the backwall type of symmetric volute is better than others.