Floating ball valve
Floating ball valves do not have a trunnion to support the ball at the bottom. Floating balls allow better sealing and less wear on the valve seat. These valves are commonly used in low pressure applications
The floating ball valves are operated by a shaft attached to the top of the ball and rotates it 90 degrees (what is called quarter turn). As the ball rotates, the bore opens or closes, releasing or stopping the flow of fluid. As the ball rotates on its stem, the flow pressure pushes the ball against its seat downstream, creating a tight seal. Thus, floating ball valves may not seal as effectively in very low pressure applications after some seat wear has occurred. This is because there may not be enough pressure to push the ball into the seat downstream to create a watertight seal. However, in most applications downstream pressure is enough to maintain a tight seal long after the seats have begun to wear.