Ball valve
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A ball valve (like the butterfly valve and plug valve are one of the family of valves called quarter turn valves) is a valve that opens by turning a handle attached to a ball inside the valve. The ball has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, 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.
Ball valves 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, pressures up to 10,000 psi, temperatures up to 200 Deg C. Sizes from 1/4" to 12" are readily available They are easy to repair, operate manually or by actuators.
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.
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[edit] Types of ball valve
There are four general body styles of ball valves: single body, split body, top entry, and welded.
There are four general types of ball valves: full port, standard port, reduced port, and v port.
- A full port 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.
- A standard port ball valve is usually less expensive, but has a smaller ball and a correspondingly smaller port. Flow through this valve is one pipe size smaller than the valve's pipe size resulting in slightly restricted flow.
- In reduced port ball valves, flow through the valve is one pipe size smaller than the valve's pipe size resulting in restricted 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 4" and above 600 psi and above)
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 (electric) 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.
[edit] Straight through, two way, or three way ball valves
Three-way ball valves have an L- or T-shaped hole through the middle. The different combinations of flow are shown in the picture.
Multi port ball valves with 4 or more ways 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 by rotating a single lever operated 4 way ball valve. This 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. The 3 piece design allows for the center part of the valve containing the ball, stem & seats to be easily removed from the pipeline. This facilitates efficient cleaning of deposited sediments, replacement of seats and gland packings, polishing out of small scratches on the ball, all this without removing the pipes from the valve body. The design concept of a three piece valve is for it to be repairable.
[edit] UK terminology
Note that in common parlance in the UK a "ball valve" is used to mean a "float valve"/ballcock (as found in toilet cisterns and attic tanks). What are called "ball valves" on this page are sometimes known as "ball-o-fixes" (after the original UK market leader), although many people there do now refer to them by their corrent name.
