A ball valve is one of the simplest of valve designs, incorporating a ball-shaped port operated by a quarter-turn handle. The ball is seated within the line, and when closed, presents a surface perpendicular to the ends of the valve, stopping the flow. When open, flow is permitted through the opening in the ball. The handle is typically aligned with the position of the opening so that its status can be seen from outside the valve.
The simplicity of the ball valve is one of its greatest advantages, as the design lends itself to durability and ease of use. Ball valves are usually the valve of choice for many shutoff applications, whether the flow includes gas, liquid or liquid with suspended solids such as slurries. However, ball valves do not allow for other types of control, such as incremental flow regulation.
Types of Ball Valves
A full port ball valve features a ball that is slightly larger than the line in which it is placed, so that the opening in the ball can be of equal size to the line, thus keeping it from restricting the flow. However, this results in a larger and more expensive valve, and thus is generally not required for most construction applications.
A reduced port ball valve uses a ball that fits within the flow's parameters, resulting in an opening that is narrower than the main pipe, and a valve that fits more easily into the same space as the pipe. The flow through the valve is generally one pipe size smaller than the valve's pipe size. However, the flow discharge remains the same, since the velocity of the liquid or gas through the valve is increased as the area of flow is decreased.
A V-port ball valve employs either a V-shaped ball or a V-shaped seat, which allows the opening to be opened or closed with greater control -- the smaller end of the V opens first and gradually leads to the larger end and full flow. The design of the V-port ball valve requires a sturdier construction owing to the increased pressures at the smaller opening of the V. Often this involves a trunnion, which anchors the ball at the top and bottom of the valve.
Ball Valve Uses
The versatility of ball valves and their relatively simple construction means they are used in a wide variety of applications. A typical ball valve can endure pressures up to 10,000 psi and temperatures up to 200 degrees Celsius. They are more easily manufactured, installed and maintained than other types of valves, and can be operated manually or through the use of a pneumatic or electrical actuator. Construction materials range from metal to plastic and a variety of composites.
Ball Valve Design
Ball valves come in a variety of sizes generally ranging from 1/4 inch to 12 inches. Designs include straight-through or multi-port configurations of two, three or more outlets. The smaller sizes are usually one-piece and are designed to be discarded instead of repaired. Two or three-piece ball valves include removable stems and seats for the cleaning of deposits and or the replacement of parts without removing the entire valve from the line. The ball is placed in a matching seat to achieve uniform sealing stress, which ensures tight shut off.