Abstract: To analyze the automatic unloading of powdered materials from trucks, fluid dynamics is used to analyze the effects of two-phase fluid (a mixture of gas and powder) on the dynamic torque and bearing torque of butterfly valve opening/closing when the fluid flows at different entry speeds. Free streamline theory is also used to calculate the fluid’s contraction coefficient when it passes the butterfly valve in various opening angles. Then, the drive system of an electromagnetic actuator is built and its electromagnetic properties are analyzed in order to calculate the electromagnetic force needed to drive the butterfly valve and the correlation between electromagnetic force and current. Finally, a transient analysis of a first-order circuit is used to study R-L circuits and calculate the effects caused by the offset of actuator armature on current fluctuation. Then, a nonlinear analysis of a system made up of a butterfly valve and its electromagnetic actuator is conducted on the basis of mechanical dynamic theory. Different fluid speeds are set for the fluid entering the butterfly valve, and Simulink is used for numerical simulation. Butterfly valve opening/closing speed and the rules governing the angle of the valve opening are analyzed to obtain basic parameters that can result in less current fluctuation and steadier valve rotation speed in the automatic unloading system.