- Ball valves consist of a smooth shiny metallic or plastic ball locked in a smooth cavity with a ring shaped seal on either side of the ball concentric with the entry and exit ports of the valve. The ball has open bore or port through the middle of the ball in only one direction. A handle is connected through the side of the valve to the ball with a sealed valve stem shaft. When the valve is off, the port is perpendicular to the pipeline containing the valve, and flow is completely blocked.
- Valve operation is intuitive--when the handle is perpendicular to the direction of the pipe, flow is shut off. When the handle is turned to be parallel to the pipeline, the ball also turns 90 degrees and the port opens one end of the valve to the other and flow is virtually unrestricted from one side of the valve to the other.
- While they are primarily designed for on-off service, specially designed ball valves may be used for throttling applications where some percentage of full flow may be achieved to modulate a process. Throttling versions usually have a port that has other than a uniformly round cylindrical shape. They may be V shaped or football shaped openings to allow smooth transitions from no flow to starting flow conditions. Some throttling applications may have proportional actuators with positioners that precisely drive the ball to specific opening positions.
- Because the ball is smooth, and the seals conforming and slippery, it is easy to fully open or fully close a ball valve very quickly. Since liquids are incompressible, quickly shutting a valve that is allowing a rapid flow rate may cause water hammering, where all the momentum of the fluid is suddenly slammed into the closed valve, which sends an violent pressure wave back up the pipe which can damage it or equipment connected to it. For that reason, critical high flow applications use dampeners to restrict opening and closing rates, so that the moving liquid accelerates and decelerates smoothly and slowly.
- Since ball valves are simple, reliable and shut off tightly, they accommodate any on-off and many throttling applications. They can easily be made of any material which lends them to simple water and gas applications along with difficult situations with corrosive chemicals.
