What is a Butterfly Valve? Working Principle & Function
Butterfly Valves stop, regulate, and start flow using a quarter-turn circular action. The valve is entirely closed or opened by rotating the handle 90 degrees. Large butterfly valves are industrial equipment that typically include a gearbox, which is a mechanism that uses gears to connect a handwheel to a stem. Butterfly valves have several advantages over their competitors, including longer operating life, lower pressure drop, ease of operation, adaptability, lightness, physical size, and lower cost. Butterfly valves are typically 40% less expensive than iron gate valves, not only in terms of the purchase price but also in terms of installation. Butterfly valves with correct installation are nearly self-cleaning and have a lower risk of failure due to debris buildup. A high-performance butterfly valve that has been appropriately sized, measured, and chosen will certainly provide reliable and accurate fluid flow to the specified system. To enhance plant efficiency, the appropriate size and measurement of a butterfly valve are critical. This comes after a significant boost in your company's profitability and return on investment.
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What is Butterfly Valve?
Butterfly valves are quarter-turn rotating motion valves used in pipelines to shut off flow. A butterfly is a disk attached to a rod. The disc closes when the rod rotates it a quarter turn perpendicular to the direction of flow. Flow is allowed through the valve when it's opened by rotating the disk backward.
Basics of Butterfly Valves
Often, butterfly valves are said to be used to regulate flow. Our recommendation is not to do so since it can damage the valve disk and negatively affect the sealing properties. Their applications range from the water supply, collection, and distribution to pumping stations, and all have a broad range of uses, but flow isolation accounts for a large part of their use. Their key advantage over other valve families is their simple construction and compactness, which results in lighter weight, lower cost, and smaller installation footprints as well as faster actuation speeds.
Working Principle of a Butterfly Valve
Butterfly valves are relatively simple devices, with the valve disc rotating to control the flow of fluid. The disc closes the valve bore in its closed position, while in its open position, it is angled perpendicular to the flow direction to allow flow. Butterfly valves can be used for both bi-directional flow and shutoff. These tools, however, do not have a full bore, which makes them ineffective for pigging or swabbing. A powder coat of epoxy is applied to both the internal and external surfaces of the ductile iron body. Valve operation depends on the specific application requirement and technical specifications and may be controlled by handwheels, gears, actuators, or a combination of these. Actuation methods will be discussed later in the article.
Butterfly Valve Actuation
Butterfly valves can be operated in a variety of ways, either manually, semi-manually, or automatically.
- Electric: The valve is controlled by a 4-20mA control signal via an electric actuator, typically used for time-critical applications that require high precision regulation.
- Pneumatic: This type of actuator uses compressed air and is ideal for high-precision applications.
- Hydraulic: It is generally used in applications that require large torques to open and close the valve, such as high pressure or high viscosity purposes.
- Manual: Butter valves that are operated manually are operated by handwheels, cranks, or levers. Most smaller manual valves have levers. On larger sizes, handwheels are provided with a gearbox to transmit torque mechanically with a high advantage. An alternative means of manual actuation is installed in buried applications where there is no manhole; in such cases, the actuator is operated with a spindle extension, an adapter, and a T-key from the level ground.
Butterfly valves have lower torque requirements than other valves, such as gate valves, so sizing and installing actuators is less expensive.
Components of a Butterfly Valve
The major components of a butterfly valve are as follows:
Fitting between the pipe flanges is the valve body - flanged, double-lug, and wafer connections are the most common.
There is a disc attached to the valve body that acts as a gate to stop or throttle fluid flow; this can be compared to a gate on a gate valve or a ball on a ball valve. Bores are usually cut into the disc so that the stem, or shaft, can be received. In order to enhance flow, sealing, and/or operating torque conditions, many variations in disc design, orientation, and material are available.
Internally, the valve body is lined with a strong elastomer or metallic anti-leak seal that holds the disc firmly in place in the closed position to achieve a complete shutoff.
Valve shafts, also known as stems, are the components that connect the disc to the actuator mechanism and transmit torque through themselves.
Valve seals are present at multiple interfaces to either maintain a tight seal during operation or isolate the process medium from the internal components of the valve for a more flexible and cost-effective design.
Discs are sealed on the seat face with a continuous T-profile resilient sealing ring which is held by a retaining ring on the periphery of the disc to prevent it from rolling out. A tight seal is provided both upstream and downstream when the sealing ring is pressed against the seat face in the closed position. The double eccentric disc design allows the sealing ring to be completely unstressed in the open position.
Multiple O-ring shaft sealing eliminates any interaction between the process media and the stem/shaft, ensuring a long-term, maintenance-free seal. In addition, there are smaller, more common components like bushings, bearings, and fasteners that constitute the majority of other valve constructions.
Function of a Butterfly Valve
By regulating flow, a butterfly valve starts, slows, or stops media. The disk rotates 90 degrees and opens and closes with low torque for use with any compatible application. In general, butterfly valves are preferred over other types of valves because they cost less and are lighter in weight.
Usage of Butterfly Valves
The butterfly valve is used in applications with limited space. Butterfly valves, unlike gate valves, can be used to control flow as well as fully open and fully closed positions. In comparison to a gate valve, a butterfly valve has a small pressure loss.
Common Applications of Butterfly Valves
A butterfly valve is utilized to interrupt product flow (solid, liquid, gas) in some industries, including:
- Pharmaceutical industry
- Chemical industry
- Food industry
- Petroleum industry.
CGMP guidelines (current good manufacturing practices) are usually followed when manufacturing valves used in these industries. Due to their low cost and ease of installation, butterfly valves have replaced ball valves in many industries, especially petroleum, but they cannot be 'pigged' for cleaning.
Advantages of Butterfly Valves
Butterfly valves might offer a number of advantages over other valve types:
- Lightweight and Compact: Due to their compact design and small face-to-face dimensions, butterfly valves have considerably smaller installation space and lower installation costs, such as labor, equipment, and piping.
- Low Maintenance Requirements: Simple, economical design with fewer moving parts and therefore fewer wear points leads to significantly reduced maintenance needs.
- Fast Acting: When the handle or actuator is rotated 90°, a complete closure or opening of the valve is provided. Normally, large butterfly valves require a gearbox as part of the actuation mechanism, reducing the operational torque and simplifying the operation of the valve but sacrificing speed.
- Low Cost: Because butterfly valves are so simple in design, they require less material, are simpler to manufacture and are often more cost-effective than other valves. Cost savings are primarily achieved with larger valves.
- Versatility: Butterfly valves can be used in a wide variety of applications, including underground installations.
FAQ about Butterfly Valve
- How Do Butterfly Valves Work?
Butterfly valves belong to the family of valves known as quarter-turn valves. By turning the disc, the valve is closed so that all passageways are blocked. The disc of the valve is rotated a quarter turn when it is fully open so that the fluid can pass almost unrestricted through it.
- What Are Butterfly Valves Used for?
The application side of butterfly valves lends itself particularly well to handling large volumes of fluid, such as in water distribution systems (pump stations and water collection and transmission) and water treatment plants (seawater or raw water).