Abstract： The startup transient characteristics of a mixed flow pump with a hydraulic controlled butterfly was predicted using the unsteady numerical approach based on the method of sliding grid to realize the opening rule of butterfly valve after the establishment of the whole flow system geometrical model of the pump station. Then the external characteristics of the pump unit and static pressure at monitoring points against time as well as the internal flow transient changes were obtained. Numerical results show that the maximum reverse speed of the starting process of the unit is 0.16 times the rated speed, and the highest pressure in the pump outlet is 1.26 times the rated value, and neither of them exceeds the permissible value. When the unit speed shows a stable tendency, the flow characteristics and the pressure gradient change in the pump are mainly affected by the butterfly valve opening. While at the small opening , the pressure gradient in the pump is larger, and the maximum differential pressure reaches 456 m(1.62 times the rated lift). The high pressure water flows through the butterfly valve in the form of the jet and generates a backflow on the outlet side, which results in a drastic fluctuation of the differential pressure on both sides of the butterfly valve and easily induces the vibration of the valve body.
