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A ball valve is a valve which operates using a spherical ball with a hole (also known as a bore) through the middle. When the valve handle is turned, the ball rotates to align the bore with the flow path—allowing fluid to pass through. When turned 90 degrees, the solid side of the ball blocks the flow entirely, creating an airtight seal. The handle lies flat in alignment with the flow when open, and is perpendicular to it when closed, making for easy visual confirmation of the valve's status. The shut position 1/4 turn could be in either clockwise or counter-clockwise direction.
Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff and control applications, where they are often preferred to gate valve and globe valve valves, but they lack the fine control of those alternatives, in throttling applications.
The ball valve's ease of operation, repair, and versatility lend it to extensive industrial use, supporting up to and up to , depending on design and materials used. Sizes typically range from 0.2 to 48 in (5 to 1200 mm). Valve bodies are made of metal, plastic, or metal with a ceramic; floating balls are often chrome plating for durability. One disadvantage of a ball valve is that when used for controlling water flow, they trap water in the center cavity while in the closed position. In the event of ambient temperatures falling below freezing point, the sides can crack due to the expansion associated with ice formation. Some means of insulation or heat tape in this situation will usually prevent damage. Another option for cold climates is the "freeze tolerant ball valve". This style of ball valve incorporates a freeze plug in the side so in the event of a freeze-up, the freeze plug ruptures, acting as a 'sacrificial' fail point, allowing an easier repair. Instead of replacing the whole valve, all that is required is the fitting of a new freeze plug.
For cryogenic fluids, or product that may expand inside of the ball, there is a vent drilled into the upstream side of the valve. This is referred to as a vented ball.
A ball valve should not be confused with a "ball-check valve", a type of check valve that uses a solid ball to prevent undesired backflow.
Other types of quarter-turn valves include the butterfly valve and plug valve and freeze proof ball valve.
The one-piece bodies provide a very rigid construction, in some versions the ball is removable from the valve without taking the entire valve out of the line however multi-piece bodies offer greater scope for ingenuity of design.
In addition, there are different styles related to the bore of the ball mechanism itself. And depending on the working pressure, the ball valves are categorized as low-pressure ball valves and high-pressure ball valves. In most industries, the ball valves with working pressures higher than are considered high-pressure ball valves. Usually the maximum working pressure for the high-pressure ball valves is and depends on the structure, sizes and sealing materials. The maximum working pressure of high-pressure ball valves can be up to . High-pressure ball valves are often used in hydraulic systems, so they are also known as hydraulic ball valves.
Ball valves in sizes up to generally come in a single piece, two or three-piece designs. One-piece ball valves are almost always reduced bore, are relatively inexpensive, and are generally replaced instead of repaired. Two-piece ball valves generally have a slightly reduced (or standard) bore, and can be either throw-away or repairable. The three-piece design allows for the center part of the valve containing the ball, stem and 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. Each valve is heated to a certain degree, while the excess material is trimmed from the body.
There are a few types of ball valves related to the attachment and lateral movement of the ball:
A floating ball valve is one where the ball is not held in place by a trunnion. In normal operation, this will cause the ball to float downstream slightly. This causes the seating mechanism to compress under the ball pressing against it. Furthermore, in some types, in the event of some force causing the seat mechanism to dissipate (such as extreme heat from fire outside the valve), the ball will float all the way to metal body which is designed to seal against the ball providing a somewhat failsafe design.
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, hydraulically or Electric 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.
There are many different types of seats and seals that are used in ball valves as well. Valves are usually manufactured with different materials, each with specific applications they are good for due to their chemical compatibility, pressures, and temperatures. Some of the commonly used materials include brass, stainless steel, bronze etc. These material choices ensure that valves are suitable for their respective functions, providing efficient and reliable performance in various industries and applications.
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