<br>Butterfly valves, also known as rotary disc valves, are quarter-turn rotational motion valves used to regulate flow in a pipeline. Their simple design, relatively low cost, and ease of operation make them a popular choice across a wide range of industries and applications. This report provides a detailed study of butterfly valves, covering their construction, working principle, types, advantages, disadvantages, applications, and selection criteria.
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<br>Construction:
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<br>A butterfly valve consists of a disc positioned in the center of the pipe. The disc is connected to a stem, which passes through the disc and is connected to an actuator on the outside of the valve. The actuator rotates the stem, which in turn rotates the disc. When the disc is parallel to the flow direction, the valve is fully open, allowing unobstructed flow. When the disc is perpendicular to the flow direction, the valve is fully closed, blocking the flow. Intermediate positions allow for throttling the flow.
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<br>Key components of a butterfly valve include:
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<br> Body: The valve body provides the structural support and houses the disc and stem. It is typically made of cast iron, ductile iron, carbon steel, stainless steel, or plastic, depending on the application and fluid compatibility.
Disc: The disc is the flow control element. It can be made of the same materials as the body, or of different materials to provide specific corrosion resistance or wear resistance.
Stem: The stem transmits the rotational motion from the actuator to the disc. It is typically made of stainless steel or other corrosion-resistant materials.
Seat: The seat provides a tight seal between the disc and the body when the valve is closed. Seats can be made of resilient materials like elastomers (e.g., EPDM, Buna-N, Viton) or metal.
Actuator: The actuator is the mechanism that rotates the stem. Actuators can be manual (lever or gear operated), pneumatic, electric, or hydraulic.
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<br>Working Principle:
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<br>The operation of a butterfly valve is based on the rotation of the disc within the valve body. When the actuator rotates the stem, the disc rotates accordingly. The angle of the disc determines the flow rate through the valve.
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<br> Open Position: When the disc is parallel to the flow direction (0 degrees), the valve is fully open, and the flow is unobstructed. The pressure drop across the valve is minimal.
Closed Position: When the disc is perpendicular to the flow direction (90 degrees), the valve is fully closed, and the flow is blocked.
Throttling: By positioning the disc at intermediate angles, the flow can be throttled or regulated. However, prolonged throttling can lead to erosion of the disc and seat, especially at high flow velocities.
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<br>Types of Butterfly Valves:
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<br>Butterfly valves are available in various designs, each suited for specific applications. The main types include:
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<br> Wafer Butterfly Valve: This is the most common type. It is designed to fit between two flanges. The valve body has holes that align with the flange bolts, securing the valve in place. Wafer valves are typically used for lower pressure applications.
Lug Butterfly Valve: Lug valves have threaded inserts (lugs) around the valve body, allowing them to be bolted directly to the flanges. This design allows for disconnecting one side of the piping system without disturbing the other side. Lug valves are suitable for higher pressure applications and dead-end service.
Flanged Butterfly Valve: Flanged valves have flanges on both ends that match the piping flanges. This design provides a strong and reliable connection. Flanged valves are used for high-pressure and high-temperature applications.
High-Performance Butterfly Valve: These valves are designed for demanding applications requiring tight shutoff and high pressure capabilities. They often feature offset disc designs and metal seats.
Triple Offset Butterfly Valve (TOBV): TOBVs have a unique disc design with three offsets. This design eliminates rubbing between the disc and the seat, resulting in longer seat life, tighter shutoff, and suitability for high-pressure and high-temperature applications.
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<br>Advantages of Butterfly Valves:
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<br> Low Cost: Butterfly valves are generally less expensive than other types of valves, such as ball valves or gate valves, especially in larger sizes.
Compact Design: Their compact and lightweight design makes them easy to install and maintain, especially in space-constrained environments.
Quick Operation: The quarter-turn operation allows for quick opening and closing, making them suitable for applications requiring rapid flow control.
Low Pressure Drop: When fully open, butterfly valves offer relatively low pressure drop compared to other valve types.
Versatility: They can be used with a wide range of fluids and in various applications.
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<br>Disadvantages of Butterfly Valves:
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<br> Throttling Limitations: Prolonged throttling can lead to erosion of the disc and seat.
Pressure Limitations: Standard butterfly valves are generally not suitable for very high-pressure applications.
Cavitation: At certain flow conditions, cavitation can occur, which can damage the valve.
Obstruction in Flow Path: The disc always presents an obstruction in the flow path, even when fully open.
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<br>Applications:
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<br>Butterfly valves are used in a wide variety of industries and applications, including:
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<br> Water and Wastewater Treatment: For flow control in pipelines.
Chemical Processing: For handling various chemicals and corrosive fluids.
Oil and Gas: For flow regulation in pipelines and processing plants.
Power Generation: For controlling steam and cooling water flow.
HVAC: For regulating airflow in heating, ventilation, and air conditioning systems.
Food and Admiralzavod.com (https://admiralzavod.com/sites/products/zatvor-diskovij-du-500-ru-25-z-gumovim-uschilnennyam) Beverage: For controlling the flow of liquids and gases in food processing plants.
Pharmaceutical: For handling sterile fluids and chemicals.
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<br>Selection Criteria:
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<br>When selecting a butterfly valve, the following factors should be considered:
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<br> Fluid Type: The fluid being handled will determine the materials of construction for the valve body, disc, and seat.
Operating Pressure and Temperature: The valve must be able to withstand the operating pressure and temperature of the system.
Flow Rate: The valve should be sized appropriately for the required flow rate.
End Connection: The end connection (wafer, lug, flanged) should be compatible with the piping system.
Actuation Type: The actuation type (manual, pneumatic, electric, hydraulic) should be selected based on the application requirements.
Shutoff Requirements: The required shutoff class will determine the type of seat material and valve design.
Cost: The cost of the valve should be considered in relation to its performance and reliability.
<br>Standards and Approvals: Ensure the valve meets relevant industry standards and approvals.
Conclusion:
<br>Butterfly valves are a versatile and cost-effective solution for flow control in a wide range of applications. Their simple design, ease of operation, and relatively low cost make them a popular choice for many industries. By carefully considering the application requirements and selecting the appropriate valve type and materials, users can ensure reliable and efficient performance. Ongoing maintenance and inspection are crucial to maximize the lifespan and performance of butterfly valves.
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