Ball valve is a quarter turn operated valve. The closure member is a spherical plug with a through hole. When the valve is in open state, the through hole is in-line with the fluid flow and hence, the fluid passes through it. The valve is closed by rotating the globe by 90 Deg. such that the hole now becomes perpendicular to the flow and hence, stops the flow.
The seat is usually circumferential, made up of soft materials to offer a tight shutoff. The seat can be made either out of plastic or metals. Ball valves are not recommended to be used in a partially open condition. Due to misalignment between the flow direction and opening of the plug, large pressure drop takes place in partially open condition.
Due to above specified challenges, ball valves are mostly used in shutoff applications. Ball valves are commonly used in steam, water, oil, gas, air, corrosive fluids. They can handle slurries and dusty dry fluids. Ball valves are not used with abrasive and fibrous materials as it poses risk of damage to the seat and plug surface.
There are two elementary designs of ball valves – the floating ball design, which depends on the valve seats to support the ball, and trunnion mounted ball, which uses the trunnion to support the ball. Trunnion mounting is used on large valves, as it can reduce the operating torque to about two-third of that provided by a floating ball.
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