The way a ball valve functions makes it easy to see if the valve is open or shut. The handle that operators use to adjust where the sphere is aligned with the flow when the valve is open, and it is perpendicular when the valve is closed. And the ball valve can be devided into many different types for different functions, such as floating ball valve, trunnion mounted ball valve, top entry ball valve, dbb ball valve, subsea ball valve, etc.

http://www.tfcvalve.com/ball-valve/dbb-ball-valve/