Ball valves are mainly used to shutt off, distribute and change the direction of fluid medium flow in pipeline. O shaped ball valves are usually used for ON-OFF applications while V shape opening has good flow adjustment function. Ball valve are generally quarter turn operated valves, i.e. needs to be operated with a rotation of 90 degrees and a small turning torque to close tightly. The completely equal valve body cavity provides a direct flow path with little resistance for flow. Ball Valves are designed as per BS 5351, API 6D, ASME B 16.34 and ISO 17292 standards.
Trunnion Mounted
Function
Ball valves are widely used for ON-OFF duty and sometimes for flow regulation as well. These valves provide little or no flow resistance and is helpful in minimising pressure drops and losses. The size of the flow path is generally constant in a linear manner throughout body and ball. This means that the flow rate does not change at any given point, provided the valve is full open. However, this is the case only with full bore (port) valves. Reduced bore valves generally have a reduced flow passage in ball and partial body sides. This results into low pressure drop and flow reduction. Ball valves have a variety of configurations and type typically 1 piece, 2 piece and 3 piece design, floating, trunnion mounted, side entry, top entry, full bore or reduced bore, etc.
Operation
Commonly ball valves ( BS 5351, API 6D, ASME B 16.34 and ISO 17292) are operated by a rotating a lever or gearbox connected handwheel coupled with stem that is fixed to the ball concealed inside body of valve. They are characterised as quarter turn. The stem is rotated 90 degree and the valve is thus operated, providing a visual indication of valve position as well. Sometimes actuators is attached to the stem on top so that it rotates the stem to operate the valve. The actuator are often are coupled into the stem from top. They may have a pointer over the actuator indicate valve position. Ball valves may have flanged ends drilled according to pipeline-compatible flange dimensional standards. Sometimes ball valves are butt welded or socket welded or threaded and installed on pipelines. Ball valves are typically constructed from cast carbon steel, stainless steel, alloy steels, and forged steels. For flow regulation, a V shaped port is preferred in ball. So the V opening of port gives a varying flow area. The varying area results in flow control which is usually calculated and termed as ‘Valve CV’ also known as ‘Co-efficient of Flow Value”.
Ball valves API 6D
Construction as per ASME B16.34
Body Type
Ball Valves are usally designed in 1 piece for smaller sizes like 0.5 inches to 2 inches preferable. Above 2 inches ( including 2″) 2 piece and 3 piece design is used. 2 piece design consist of one side piece (sometimes called adaptor) and one body which houses the ball and seat ring. 3 piece design consists of 2 side pieces which houses the seat and seat ring and a body which houses the ball, stem and trunnion support. The body are usually bolted with the side piece along with a gasket or rings to prevent leakages.
Ball support
Depending on the size and pressure rating, ball in a ball valve is either of floating type or trunnion supported type. Usually in low pressure and small sizes, balls are floating type. Ball rests itself between the seats while connected with stem at the top of ball. In high pressure and large size valves the ball is usually heavy and hence a trunnion support is provided at the bottom of ball. The trunnion is like a small shaft at bottom and sometimes are assembled with trunnion guide plates.
Bore / Port
Depending on the process requirements, Ball Valves are usually availabe in full bore (port) or reduced bore. Full bore valve flow cross sectional area is same through out the equipment whereas reduce bore valves have a reduced cross sectional area in the ball and central area. Full bore valves are normally used in oil and gas and chemical applications where pigging required. These are covered in API 6D standard.Didlink
Applications
Industrial applications such as oil and gas, petrochemicals, chemical, power generation, mining and industries use this valves. What makes this useful is that its simple operation and its ability of flow control in addition to on-off duty. There is also a pre calculated pressure drop and flow CV calculation which is as per the flow requirements of process.
Post time: Jan-28-2026