The ones in our shower have a small detent or ramp built in so it requires more pressure to get out of the valley position, but not much. You can look up gravity hinges to get a better explanation on how they work. Usually they use gravity (weight of the door helps) to bring the doors to a closed position (center). When the doors are opened, either direction they are pushed up a small incline or ramp, when released they ride back down the ramp. When at the bottom of the ramp, the doors are in the middle or closed position. With this in mind determine what is keeping them from going to the closed position. Being level is important as is proper alignment.