Which of the following is NOT a subcategory of butterfly valves?

Butterfly valves are a type of valve that uses a rotating disc to regulate fluid flow. They come in several subcategories, and understanding their variations is essential for proper application in engineering contexts.

The subcategories typically associated with butterfly valves include swing-through, lined, and high-performance types. Swing-through refers to a design that allows for the disc to "swing" open fully, providing minimal obstruction to the flow when open. Lined butterfly valves are often used to handle corrosive fluids, featuring a liner that protects the valve from damage. High-performance butterfly valves utilize advanced designs, often providing tighter sealing and handling higher pressure differentials than standard designs.

Ball valves, however, are a distinct type of valve characterized by a spherical disc that controls flow. While both butterfly and ball valves serve similar functions in controlling fluid flow, they are not interchangeable types and have different construction and operational mechanisms. Therefore, identifying the ball valve as NOT being a subcategory of butterfly valves is correct.