"Axial Fan" around the impeller hub by a number of airfoil component cascade, expanded the plane leaves the gate, the airflow channel between the blades, as indicated in 1,2,3 ....... Airflow through the rotary vane gate will produce flow separation phenomenon, but this is always the first to occur off the flow of one blade and the back surface of the water flow path of the blade, as shown in the rear of the flow passage 2 due to the occurrence of vortex flow obstruction. 2 runner due to reduced traffic congestion will flow channel adjacent to the 1,3 split, and with the original flow of the flow rate of 1,3 confluence flow path is increased. Because the bus has changed the flow conditions 1,3 runner, but also changed the direction of flow of imports 1,3 flow path. The same rotation direction of the flow channel 2 to bypass flow path direction of the impeller 1, will make the blade angle of attack is reduced while suppressing the occurrence of flow separation; contrary to the shunt flow path 2 opposite direction 3 and the direction of rotation of the impeller flow channel , blade angle of attack will increase the generation of induced off the flow.