Aug. 16, 2023
The invention of the butterfly valve has improved the processes and applications of various industries.
The butterfly valve is a mechanism that regulates the flow of materials in a large pipe diameter through a quarter-turn rotation of the disc.
A rod passes through the center of the disc, and this rod is connected to a drive that controls the movement of the disc. The position of the disc is parallel or perpendicular to the flow of the medium. The butterfly valve is different from other valves because the butterfly plate is always in the fluid, resulting in pressure changes at any position of the valve.
Some valves are named after their shapes, such as ball valves, globe valves, needle valves, etc. Other valves are named after their movement and function: gate valve, plug valve, pinch valve, life valve, slide valve, etc. The butterfly control valve is also named for its movement.
The butterfly valve gets its name because its movement is similar to that of wings in flight. The rod is similar to the body of a butterfly, and the disc moves like a butterfly's wings. The movement of a butterfly valve is similar to that when a butterfly descends, its wings move up and down in a 90-degree motion.
Plastic Lined Butterfly Valve
Stoppage of flow is accomplished by the valve disk sealing against a seat that is on the inside diameter periphery of the valve body. The intimate contact between the seating of tight shut-off butterfly valves may be achieved by various means. Some of the ones more frequently used are:
ㆍBy interference seating that requires the disc to be jammed into the seat.
ㆍBy forcing the disc against the seat, requiring the disc to tilt about a double offset hinge in a manner comparable to tilting disc check valves.
ㆍBy pressure-energized sealing using sealing elements such as O-rings, lip seals, diaphragms, and inflatable hoses.
The majority of butterfly valves are of the interference-seated type in which the seat has a rubber liner. Where rubber is incompatible with the fluid to be sealed, the liner may be made of PTFE, which is backed up by an elastomer cushion to impart resiliency to the seat.
In early designs, a metal disk was used to seal against a metal seat. This arrangement did not provide a leak-tight closure but did provide sufficient closure in some applications (i.e., water distribution lines).
The following are some characteristics for butterfly valves when used for modulating service. A valve having a stated inherent characteristic may provide a different installed characteristic due to interaction with the system.
Linear – Liner flow characteristic means the flow-rate is directly proportional to the amount of disk travel. For example, at 50% open, the flow-rate is 50% of maximum flow.
Equal percentage – Equal percentage flow characteristic means that equal increments of valve travel produce equal percentage changes in flow-rate. For example, if a valve travel change from 10% open to 20% open produced a 60% change in flow-rate, then a valve travel change from 20% open to 30% open would produce another 60% change in flow-rate.
Quick opening – Quick opening flow characteristic means that flow-rate through the valve increases very rapidly for incremental changes in valve travel when valve position is near closed. As valve position becomes more open, flow-rate changes diminish with incremental changes in valve travel approaching zero change as the valve position nears full open
The selection of the appropriate control valve characteristic is dependent on the needs of the system. Because there are several factors to be considered, a complete system analysis is required to determine precisely which is the optimum characteristic.
The butterfly valve regulates the flow by starting, decelerating, or stopping the medium. The disc opens and closes with a low torque of 90 degrees, which is suitable for any compatible application. Because of their low cost and lightweight, butterfly valves are generally more popular than other types of valves.
For some processes, extreme temperatures and corrosion are factors that can easily damage the valve seal. Butterfly valves can withstand extreme cold or extreme heat. This means that the integrity of the sealing device is critical for high-risk applications such as energy production and oil processing (because a leak may threaten public safety or the environment).
There are some standard guidelines for the positioning of butterfly valve components. The butterfly valve needs to have a certain distance from other parts, such as pumps, elbows, and another valves-6 pipe diameter separation is ideal.
Generally, the valve stem of a butterfly valve is installed vertically with the actuator directly above it, but in some cases, the valve stem is installed horizontally. When connected to a pump or check valve, the disc must have a gap to avoid interference with other nearby components.
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