The butterfly valve is a popular type of valve used to regulate flow in a variety of industries. The butterfly valve has a simple design consisting of a disc-shaped element that rotates around an axis to control flow. In the closed position, the disc blocks the valve orifice; in the open position, the disc rotates to allow flow. A quarter turn moves the valve from fully open to fully closed, or vice versa, so the butterfly valve can be opened and closed quickly.
The main function of a butterfly valve is to regulate the flow of fluid in a pipeline. The disc-shaped element can be rotated to any angle between 0 and 90 degrees, allowing precise control of flow rate. Butterfly valves are often used in on/off applications or to regulate flow. When fully open, butterfly valves have minimal pressure drop and provide unimpeded flow. When closed, they provide a tight seal, preventing any flow.
2.What are the specifications of butterfly valves?
Butterfly valves are available in a variety of sizes, materials, and designs to suit different applications. Some common specifications include:
Sizes: 2 inches to 72 inches
Pressure ratings: Class 150 to 1500
Temperature ratings: -50°C to +650°C
Body materials: cast iron, ductile iron, carbon steel, stainless steel, etc.
Disc materials: stainless steel, aluminum bronze, duplex steel, etc.
Seat materials: EPDM, Buna-N, Viton, PTFE, etc.
3.What are butterfly valves used for?
Butterfly valves are used in a variety of industries, including chemical, oil and gas, water treatment, HVAC, and food and beverage. Some common applications for butterfly valves include:
On/off and regulating control of water, steam, gas, and liquids
Isolation and regulation of pipelines, tanks, and containers
Flow rate control in HVAC systems
Fluid flow control in food and beverage processing
4.Components of a butterfly valve
Butterfly Valve Parts
The following are the main components of a butterfly valve:
Body: Installed between pipe flanges - the most common end connection types are flange, double lug and wafer types.
Disc: Attached to the valve body, acts as a gate to stop or throttle the flow; it can be considered equivalent to the gate in a gate valve or the ball in a ball valve. The disc is usually drilled to receive the valve stem or shaft. There are many variations in disc design, orientation and material to improve flow, sealing and/or operating torque. For example, Hawle's 9881k double eccentric disc is designed to reduce seal wear and "galling" as well as operating torque requirements.
Seat: The body liner is a solid elastomer or metal leak-proof seal that holds the disc in the closed position to achieve full shutoff. The stainless steel welded fillet and micro-finished one-piece seat of the 9881k series ensures that the seat surface is resistant to corrosion and erosion. With this special type of seat design, it is possible to manufacture a drip-proof valve in accordance with EN12266-A requirements.
Valve stem: Also commonly referred to as the valve stem, is the component that connects the valve disc and the actuator and transmits torque through itself.
Seals: Present at multiple interfaces within the valve to ensure a tight seal during operation or to isolate the process media from the internal components of the valve, allowing for a more flexible and cost-effective design.
The seal on the seat surface is ensured by a continuous T-shaped elastic sealing ring, which is fixed to the periphery of the valve disc by a retaining ring to prevent the sealing ring from rolling out. In the closed position, the sealing ring presses against the seat surface, providing a tight seal on the upstream and downstream ends. In the open position, the sealing ring is completely unstressed due to the double eccentric valve disc design.
The multi-O-ring shaft sealing system ensures maintenance-free sealing throughout the service life of the valve by eliminating the interaction between the process media and the valve stem/shaft. In addition, there are smaller, more common components such as bushings, bearings and fasteners, which are also part of most other valve structures. Details of some components on the drive end, such as handles, levers, gearboxes and handwheels, will be introduced in the drive section.
5.Materials used to make butterfly valves
The valve body needs to have high toughness and rigidity to protect the internal components of the butterfly valve. Likewise, the valve stem and disc must also have these characteristics to withstand fluid pressure. Butterfly valve components can be made of the following materials:
Metallic Butterfly Valves
Stainless steel is an alloy with a high chromium content (10.5-30%) and small amounts of nickel and molybdenum. It is known for its excellent strength, toughness, and resistance to corrosion and weathering. The corrosion resistance is mainly due to chromium, which forms a thin protective chromium oxide layer that prevents oxygen from penetrating into the material. If the surface is damaged, this layer can be regenerated with the help of oxygen, thus preventing rust. Molybdenum helps resist pitting corrosion.
Stainless steel butterfly valves are well suited to handling acidic and corrosive fluids over a wide range of pressures and temperatures. Austenitic stainless steels are ideal for low-temperature processes, while duplex stainless steels are suitable for higher pressures. 316 stainless steel is the preferred stainless steel grade.
Carbon Steel
Carbon steel is an alloy containing up to 2.5% carbon. It has good mechanical properties and is suitable for applications without special requirements. These valves are usually produced using a sand casting process to produce the valve body and disc. Although carbon steel butterfly valves are more cost-effective compared to stainless steel butterfly valves, they are not suitable for handling corrosive fluids.
Hastelloy Butterfly
Hastelloy Butterfly Valves are commonly used in applications involving high temperatures, high pressures, and corrosive environments, including those in oil and gas processing and power generation.
Brass
Brass is an alloy composed of copper and zinc, known for its toughness, durability, and ability to withstand high temperatures. Brass is prized for its ability to resist corrosion and biofouling, as well as its antimicrobial properties, which help prevent the growth of microorganisms and biofilms on its surface.
Nickel Alloys
Nickel alloys are known for their excellent resistance to corrosion, harsh environments, and high temperatures. They often outperform stainless steel in extremely corrosive conditions. However, nickel butterfly valves tend to be denser and more expensive.
Titanium Alloys
Titanium alloys have a high strength-to-weight ratio and are highly regarded for their resistance to corrosion and biofouling. Due to their non-toxic properties, they are suitable for use in seawater environments and water treatment applications. Despite these advantages, titanium butterfly valves are also quite expensive.
Nickel Aluminum Bronze
Nickel Aluminum Bronze is a copper-based alloy that includes 10% aluminum, 5% nickel, and 5% iron. This alloy is known for its ability to resist corrosion, bacteria, and biofouling. Nickel Aluminum Bronze butterfly valves are often used in seawater environments, such as offshore pipelines, as well as in water purification and wastewater treatment applications.
Conclusion
In conclusion, butterfly valves are widely used to regulate flow in various industries due to their simple design, cost-effectiveness, and ease of operation. Although they have some limitations, their advantages make them a popular choice for many applications. When selecting a butterfly valve, it is important to consider the specifications and requirements of the application to ensure that the valve is suitable.