Ball Valves – Amiran Petro

This type of valve has the following advantages:
• can be quickly opened and closed with a quarter turn movement
• ensure a very tight seal without the need for high torque forces
• have a compact design (this is the main difference between a ball valve and a gate valve – which are both on/off devices)
The disadvantages are:
• valve has poor regulating and throttling capabilities, as it is designed for pipeline shut-off instead of flow modulation (this is an ideal function for globe valves): throttling causes the partially exposed seat to erode because of the high-velocity flow and pressure experienced by the valve. The wear may lead to a leakage of the valve progressively.
• valve can’t be used for slurries, as the accumulation of suspended particles and debris would make the valve leak. These particles may solidify in the cavities in the proximity of the ball and seats. Ball valves are way more very efficient with gases and other liquid fluids (even challenging chemicals as dry chlorine, hydrofluoric acid or hydrochloric acid, and oxygen).
• may be difficult to clean (except for top entry design)
The open, close or partially open position of the valve can be detected by looking at the position of the lever:
• when the lever is aligned to the pipe, the valve is open; when it is perpendicular to the pipe, the valve is closed.
• when it is any other position, the valve is partly open (or partly closed) and is modulating the flow.
These valves belong to the family of “quarter turn” valves or “1/4 turn valve” (together with butterfly and plug valves), as the opening and closing operations are executed by turning a lever connected to the disc by 90 degrees.
The key ball valve specifications are the API 6D, BS 5351 (forged) and ASME B16.34 (pressure and temperature ratings), ASME B16.5/B16.47 (flanged ends) and ASME B16.25 (butt welding ends).