1. Basic structure and working principle of eccentric butterfly valves
The main difference between eccentric butterfly valves and ordinary butterfly valves lies in the design of the valve core. The eccentric design of the butterfly plate axis and the sealing surface of the eccentric butterfly valve makes the sealing performance of the valve more reliable. Eccentric designs are usually divided into single eccentric, double eccentric and triple eccentric.
1. Single eccentric: The rotation center of the butterfly plate deviates from the center of the sealing seat, which is usually used in low-pressure systems.
2. Double eccentricity: The rotation axis of the butterfly plate is offset from the center of the sealing surface, forming a double eccentricity. The double eccentricity design increases the sealing of the valve and is suitable for medium pressure occasions.
3. Triple eccentricity: In addition to the offset of the rotation axis and the sealing surface, an offset along the valve seat is added. This design makes the valve more sealing and is suitable for high pressure, high temperature and highly corrosive fluid environments.
The main working principle of the eccentric butterfly valve is to control the flow of fluid by rotating the butterfly plate. Due to the eccentric design, the contact position of the butterfly plate with the sealing surface changes when the valve is closed, thereby providing better sealing and reducing wear.
2. Key factors for purchasing eccentric butterfly valves
When purchasing eccentric butterfly valves, the following key factors need to be considered:
1. Media type
The type of media (such as water, oil, gas, steam, acidic and alkaline liquids, etc.) directly affects the material selection of the eccentric butterfly valve. For highly corrosive media, corrosion-resistant materials such as stainless steel, chromium-nickel alloy, and Hastelloy are recommended. For high-temperature fluids, high-temperature resistant materials such as alloy steel need to be selected.
2. Working pressure and temperature
Since eccentric butterfly valves are often used in high-pressure and high-temperature environments, when purchasing, it is necessary to select the appropriate valve according to the maximum working pressure and temperature range of the pipeline system. Double or triple eccentric butterfly valves can provide better sealing and pressure resistance, and are suitable for medium and high-pressure pipelines.
3. Sealing performance
The design of eccentric butterfly valves provides better sealing performance, especially in high-pressure, high-temperature or corrosive media. There are usually two types of valve sealing methods: soft sealing and hard sealing:
- Soft sealing: usually using rubber, polytetrafluoroethylene (PTFE) and other materials, suitable for low-pressure, non-corrosive media.
- Hard sealing: using metal materials as sealing surfaces, suitable for high-temperature, high-pressure, and highly corrosive media.
4. Valve body material
The valve body material of the eccentric butterfly valve directly affects its service life and performance. Common valve body materials are:
- Cast iron: suitable for general fluids, but not for high-temperature or corrosive fluids.
- Carbon steel: Suitable for general liquids or gases, but not for highly corrosive media.
- Stainless steel: Suitable for corrosive fluids and high temperature occasions.
- Alloy steel: Suitable for extremely high temperature and high pressure environments, with strong corrosion resistance.
5. Connection method
The connection methods of eccentric butterfly valves usually include flange connection, clamp connection and threaded connection, etc.:
- Flange connection: Suitable for large-diameter, high-pressure pipeline systems, easy to install.
- Clamp connection: Suitable for small and medium-diameter pipelines, with relatively simple installation and maintenance, and low cost.
- Threaded connection: Suitable for small-diameter pipelines, simple installation, and suitable for low-pressure occasions.
6. Drive mode
The drive modes of eccentric butterfly valves include manual, electric, pneumatic, etc.:
- Manual drive: Suitable for occasions with low operating frequency and low cost.
- Electric drive: Suitable for automated operation and remote control, and can achieve precise flow regulation.
- Pneumatic drive: Suitable for high-frequency opening and closing occasions, and can provide fast response.
7. Valve size and caliber
When selecting an eccentric butterfly valve, the size and flow requirements of the pipeline must be considered. Eccentric butterfly valves are generally suitable for large-diameter pipelines because of their simple structure, light weight, and are suitable for large-diameter and high-flow situations. When purchasing, you need to choose the appropriate valve caliber according to actual needs.
8. Operational characteristics
The flow regulation ability of the eccentric butterfly valve is good, but the regulation characteristics are nonlinear. If you need to accurately adjust the flow, you should choose a valve suitable for regulation, or use it in combination with other regulating equipment.
3. Common applications of eccentric butterfly valves
Eccentric butterfly valves are suitable for various occasions where fluid cutoff or regulation is required, especially in high-pressure, corrosive media or high-temperature environments. They have the following common applications:
1. Petroleum and natural gas: Eccentric butterfly valves are widely used in oil and natural gas pipeline systems for fluid control and isolation.
2. Chemical industry: In chemical production, eccentric butterfly valves are used for fluid control of high temperature, high pressure and corrosive media.
3. Water treatment system: used for flow control, valve cut-off and fluid control in drainage systems in sewage treatment plants.
4. Power industry: Eccentric butterfly valves are used for steam control, gas flow control and delivery systems in thermal power, nuclear power plants and other fields.
5. HVAC system: In HVAC systems, eccentric butterfly valves are used for air volume regulation and temperature control.
4. Selection case of eccentric butterfly valves
Suppose a chemical plant needs to purchase eccentric butterfly valves to control the flow of corrosive chemical media, and the media works at a higher temperature. The valve needs to have strong sealing and corrosion resistance. The following points can be considered when selecting:
- Material: Use stainless steel or alloy steel to ensure that the valve is corrosion-resistant and high-temperature resistant.
- Sealing method: Use metal hard sealing to provide better sealing performance.
- Structural form: Choose double eccentric or triple eccentric butterfly valves to improve sealing and pressure resistance.
- Drive mode: Consider electric drive to achieve automatic operation.
- Flange connection: Choose flange connection to ensure that the valve can withstand high pressure and is easy to install.
5. Conclusion
Due to its unique eccentric design, the eccentric butterfly valve provides stronger sealing and durability, and is suitable for high-pressure, high-temperature and highly corrosive fluid control occasions. When purchasing, it is necessary to consider a variety of factors such as fluid properties, working pressure and temperature, sealing requirements, and valve body material. By choosing the right material, sealing method, and drive method, you can provide a reliable flow control and fluid isolation solution for the system.