Instrumentation Piping Valves

Ball valves

The concept of a ball valve dates back to ancient times. However modern ball valves have been developed during the early 20th century. Ball valves are among the least expensive and most widely used valves. Basic design of a ball valve is similar to that of a plug valve and ball valves are sometimes also known as 'spherical plug valves'. Instead of a plug, ball valve uses a spherical ball sandwiched between two sealing rings in a simple body. This ball has a hole to allow the fluid flow through it. When the valve is closed, positive isolation is provided by the sealing rings which can isolate the flow from both sides of the valve.

Rotating the ball valve by 900 can completely close or open the flow through a ball valve. Normally the handle of the valve, used to rotate the ball, is in line with the axis of the valve when it is in the open position and at right angles to the valve axis when valve is in the closed position. Since the friction involved in rotation of the ball is only generated between the ball and the sealing rings, the frictional resistance is low. Hence the torque required to rotate the valve is also low. Generally, large ball valves can be operated using a handwheel with reduction gearing.

Ball valves are produced in top-entry and split-body fashion for the ease of valve assembly. Generally these valves are produced with soft non metallic seats. PTFE, graphite, steel powder, glass are some of the common materials used for this purpose. However metallic sealing rings maybe preferred for handling of abrasive fluids or high pressure, high temperature applications.

Multiport Valves

Ball valves can also be used in the form of multiport valves as indicated in the figures below.

3 Way – 2 Port valve

3 Way – 3 Port Valve
4 Way – 4 Port valve

Advantages

Ball valves provide a leak-tight service. They can be quickly opened or closed, with a small torque. They are smaller and lighter compared to other valves for isolation. Soft seated ball valves can be used for clean applications and metallic seated valves for slurry applications. Ball valve design is flexible with several varieties. Multiport ball valves offer design options not possible with other valves.

Disadvantages

Ball valves are not very useful for throttling operations. Soft seated valves used in abrasive or slurry applications result in damage of the valve.

Applications of ball valves

  • Shut-down and isolation valves for liquid and gaseous services needing leaktight valves.
  • Emergency Shut Down valves.
  • Low differential pressure control valves.
  • Control and shut-down valves for steam service.
  • Vent and drain valves for liquid and gaseous services.
  • Pipeline surge control valves.

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