Ball valves are stop valves used to enable or block fluid flow through rotating balls with internal 900-percent bores. Using actuators, it is possible to operate a ball valve either remotely or via a controller (using a V-sector ball valve) such that it could be used as a closed-loop ball or shut-off automatic or isolated valve, or a proportional control valve. A ball valve is classified as a one-fourth-turn closed-loop valve or an isolation valve, which controls the flow of a liquid or gas through a ball shaped object that has a hole bored through its center, held in place in the valve body by two identical seats sealing off the hole.

The term ball valve refers to the fact that the inner mechanism used to alter the flow through the device is a spherical ball with a hole bored through it, serving as the flow control for the valve. The ball is the flow-control mechanism of the ball valve, and is a ball through which has been bored out a hole or tunnel in order to allow the fluid to pass through when oriented with the hole facing in line with the flow direction of the fluid. When the valve is opened, the hole is oriented in the direction of the flow, and closed when turned 90deg by a hand crank or actuation. If a hole or port is in line with the tube, the flow continues to pass the valve; if a hole is perpendicular to the tube, flow stops at the valve.

In reducing port ball valves (more commonly known as reducing bore) the flow through the valve is a size smaller than the diameter of the pipe the valve is in, which results in the flow area being smaller than the size of the pipe. Reduced port ball valves have a bore size one to two nominal sizes smaller, providing a narrower flow path, which is typically used where loss of power is not a concern, such as in shunt or relief valves.

Ball valves have a port that has a round section that is the same diameter as the pipe; thus, the flow does not turbulence, which in turn decreases pressure loss. Since only one-fourth of a turn is required to completely close or open, a ball valve restricts or allows the flow at once.

Full-bore ball valves are also used for transporting fluids containing mixed solids, where flow restrictions result in particle accumulation, which may ultimately result in the separation of the mixture flowing through them. Full bore ball valves are typically used in throttling applications in a variety of systems where flow rates are high and pressure differences are low. The area of fluid flow remains constant with full bore valves, so flow resistance offered by this type is very low. The high speed of the fluid used in such ball valves forces designers to devise usually stronger designs for them, as these types of fluids will damage the standard valve rapidly.

At higher fluid pressures, the seats may deform due to pressure applied by floating balls, which may impact on the valves sealing characteristics under lower pressures. The rotating ball during the operation continuously cleans the surface and thus removes contaminants that can lead to leaking of the normal valve. The valve shaft allows for limited sideways movement for the ball, generated by the pressure against the ball from upstream. The simplicity, reliability, and versatility of a ball valve make it widely used in industry, supporting up to 1000 bars (100 MPa; 15,000 PSI) of pressure, and temperatures as high as 752degF (400degC), depending on design and materials used.
Ball valves are mechanical devices that can control, direct, direct, and modulate the flow of different substances, such as gases, pressures, liquids, etc. There are various types of ball valves, with various designs for particular uses, but basic parts of the ball valve are similar between them. As stated in the start of this article, ball valves are primarily suited to shutdown utility applications, though certain designs, like V-port ball valves, do have the ability to regulate the flow. The ball valve is economical and may be used for applications where precision in the control of flow is not required.

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