A ball valve is a flow control device which operates using a spherical ball with a hole (also known as a bore) through the middle. When the valve handle is turned, the ball rotates to align the bore with the flow path—allowing fluid to pass through. When turned 90 degrees, the solid side of the ball blocks the flow entirely, creating an airtight seal. By convention, the handle lies flat in alignment with the flow when open and is perpendicular to it when closed, making for easy visual confirmation of the valve's status. The shut position 1/4 turn could be in either clockwise or counter-clockwise direction.
Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff and control applications, where they are often preferred to gates and globe valves, but they lack the fine control of those alternatives in throttling applications.
