A couple moment is produced when a network of forces do not have a resultant force, but only produces moment. As a result, it induces rotation without translation. That means the two forces are equal.
Moment = Force * Distance
In order to determine the vertical force, we must know the distance between the two forces which is represented by the length of the pipe. Suppose the pipe is 0.5 m, then the force is
400 N·m = F*0.5 m
F = 800 N