Two dislocations of opposite signs interacting via their elastic fields are consider. They move in parallel slip planes in a PSB channel. Initially they are kept apart in straight screw positions. The walls of the channel are simulated as the elastic eld of rigid edge dipoles. The dislocations are modeled as plane curves. A special computer program based on the owing volume method and the method of lines is employed. Assuming an over-damped motion, we consider a linear relationship between the force acting on the dislocation and the velocity magnitude. The computation simulates the shape changes of the dislocations during their passing. The passing stress for various distances between the slip planes and for various channel width is compared with the bowing stress. The stress and strain controlled regimes of the dislocation motion are analyzed.