Floating Ball Valve
The stem is connected to a slot at the top of the ball which allows the ball to rotate a quarter turn (90 degrees). The shaft allows for a certain amount of lateral movement of the ball that is generated from the upstream pressure acting on the ball. This small lateral movement, in fact, produces a load on the ball that presses it against the downstream seat which improves leak tightness of valve. This type of valve design is capable of bi-directional shut-off. The floating valve is very difficult to operate when upstream pressure is high. You can see the image of a floating type valve.