A ball valve is a type of shut-off valve used to control the flow of gas or liquids, by means of a perforated, hollow, rotating ball. The valve is opened or closed when the ball is rotated by a quarter turn (90°), allowing the medium to flow through or be blocked. They are characteristically very durable, continuing to perform well over long periods and providing a reliable seal, even for contaminated media or after a long period of inactivity.
Ball valves come in five general body types, depending on how the valve components are manufactured and put together, although the operation remains the same. Single-piece balls are generally for sizes up to 2 inches and almost always have a reduced bore, while 2-piece ball valves may have a standard or slightly reduced bore. Single-piece ball valves are fairly cheap and often disposable, with 2-piece valves having a repair option. A 3-piece ball valve is intended to be repairable, and is designed so that the centre part with the ball components can be easily removed for cleaning.
There are also different bores for the mechanism, dependent on its working pressure, so that ball valves are often divided into low and high pressure versions (greater than 3,000 psi). According to their size, structure and sealing materials, high pressure ball valves can operate at up to 15,000 psi. These ball valves are mostly commonly used in high pressure applications such as hydraulic systems, and are also called hydraulic ball valves.