Ball Valves

Ball Valve General Infomation

Ball Valves are valves with a spherical disc and the part of the valve which controls the flow through it. The sphere has a port (or opening) through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is in the closed position, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle (*or lever) will be inline with the port position letting you 'see' the valve's position. The ball valve plus the butterfly valve and plug valve, are part of the family of quarter turn valves.

Ball valves very are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose). They do not offer the fine control that may be necessary in throttling applications but are sometimes used for this purpose.

Ball valves are used extensively in industry because they are very versatile, supporting pressures up to 700 bars and temperatures up to 200degC. Sizes typically range from 0.5 cm to 30 cm. They are easy to repair and operate. The body of ball valves may be made of metal, plastic or metal with a ceramic center. The ball is often chrome plated to make it more durable. There are five general body styles of ball valves: single body, three piece body,split body, top entry, and welded.

Duplex Ball Valve

There are 3 general types of ball valves according to bore:

- A full port (normally referred to as full bore ball valve) has an over sized ball so that the hole in the ball is the same size as the pipeline resulting in lower friction loss. Flow is unrestricted, but the valve is larger. This is not required for general industrial applications as all types of valves used in industry like gate valves, plug valves, butterfly valves, etc have restrictions across the flow and does not permit full flow. This leads to excessive costs for full bore ball valves and is generally an unnecessary cost. Full bore ball valves are typically used in pipelines which require pigging.

- In reduced port or more commonly known reduced bore ball valves, flow through the valve is one pipe size smaller than the valve's pipe size resulting in flow area becoming lesser than pipe. But the flow discharge remains constant as it is a multiplier factor of flow discharge (Q) is equal to area of flow (A) into velocity (V). A1V1 = A2V2; the velocity increases with reduced area of flow and decreases with increased area of flow.

- A V-port ball valve has either a 'v' shaped ball or a 'v' shaped seat. This allows the orifice to be opened and closed in a more controlled manner with a closer to linear flow characteristic. When the valve is in the closed position and opening is commenced the small end of the 'v' is opened first allowing stable flow control during this stage. This type of design requires a generally more robust construction due to higher velocities of the fluids, which would quickly damage a standard valve.

- A Trunnion Ball Valve has a mechanical means of anchoring the ball at the top and the bottom, this design is usually applied on larger and higher pressure valves (say, above 10 cm and 40 bars).

Manually operated ball valves can be closed quickly and thus there is a danger of water hammer. Some ball valves are equipped with an actuator that may be pneumatically or motor operated. These valves can be used either for on/off or flow control. A pneumatic flow control valve is also equipped with a positioner which transforms the control signal into actuator position and valve opening accordingly.

Ball Valves - Straight Through Ball Valve, Two Way Ball Valve, or Three Way Ball Valve

Three-way ball valves have an L- or T-shaped hole through the middle. There are different combinations of flow.

Multi-port ball valves with 4 ways, or more, are also commercially available, the inlet way often being orthogonal to the plane of the outlets. For special applications, such as driving air-powered motors from forward to reverse, the operation is performed by rotating a single lever 4-way ball valve. The 4-way valve has two L-shaped ports in the ball that do not interconnect, sometimes referred to as an "X" port.

Ball valves in sizes up to 2 inch generally come in single piece, two or three piece designs. One piece ball valves are almost always reduced bore, are relatively inexpensive and generally are throw-away. Two piece ball valves are generally slightly reduced (or standard) bore, they can be either throw-away or repairable.

Cavity Filler Ball Valve

Many industries encounter problem of residues in the ball valve. These residues contaminate operation of the ball valve. In cases where the fluid is meant for human consumption, it becomes all the more dangerous as it may contaminate and make the fluid toxic. In cases where the media changes from time to time, such as color of paints, the residual paint contaminates and changes the colour.

It is therefore necessary to eliminate the deposition of this residue material. The reason why this residue deposits itself in the ball valve is because of the design of the valve. During the half open position of the ball valve, a gap is created between the ball bore and the body. The fluid can easily creep into this gap and get itself deposited in this cavity of the body. To avoid the fluid getting into this cavity, the cavity has to be plugged. This can be done by extending the seats in such a manner that it is always in contact with the ball, thus avoiding the gap. This type of ball valve is known as Cavity Filler Ball Valve.

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