Selected Valve - Butterfly Valve
Butterfly valves are highly efficient and economical fluid control devices, widely used in industrial production. When selecting a butterfly valve, first ensure its performance matches the application requirements. Ease of operation and cost-effectiveness are also crucial. Consider the media characteristics, operating conditions, and sealing requirements. The specific steps are as follows:
1. Consider the fluid (media) characteristics. For liquids, the flow rate should generally not exceed 5 m/s to avoid cavitation. For corrosive media, corrosion-resistant materials (such as stainless steel or polytetrafluoroethylene) should be used.
2. Temperature and pressure ratings. Select the valve body material based on the media temperature (e.g., ductile iron for temperatures ≤ 350°C, stainless steel for high temperatures and high pressures). The pressure rating should match the nominal pressure.
3. Select the butterfly valve type. Centerline butterfly valves (common): also known as concentric butterfly valves, are suitable for low-pressure, large-diameter applications with low leakage requirements (such as water and air conditioning). They generally offer high sealing performance and low cost.
Double eccentric butterfly valves: Suitable for medium-pressure applications requiring a long lifespan, they reduce seat friction and extend valve life. Triple-eccentric butterfly valves are suitable for high pressure and demanding operating conditions, such as high temperature or highly corrosive environments. The triple-eccentric structure not only provides a tighter seal as it closes, resulting in superior sealing performance, but also reduces operating torque, improving valve efficiency and reliability.
4. Determine the butterfly valve's actuation method. Manual operation: Direct operation via a handwheel or wrench is suitable for infrequent adjustments. It is particularly suitable for small diameters and infrequent operation. Electric operation: Used in applications requiring remote control or automated systems, it can be easily integrated with other control devices for high automation. Pneumatic operation: Suitable for applications requiring fast response and high operating force, especially for emergency shutoff or safety-related applications.
5. Choose the appropriate sealing surface material. Hard seals, such as metal rings (for high temperature and high pressure), are suitable for high temperature and high pressure applications. Soft seals, such as rubber (for clean water/air) and polytetrafluoroethylene (for high corrosion), are suitable for corrosive, highly toxic, and highly hazardous media.
6. Consider the connection method. Wafer connections are easy to install and relatively low cost, making them widely used in small-diameter pipes. Flange connections are suitable for large-diameter and high-pressure pipes. Clamp connections are common for quick assembly in the food industry.
VII. Material Selection: The butterfly valve body material should be selected based on the media characteristics and operating conditions. Common materials include ductile iron (for normal-temperature water), cast steel (for medium- and high-pressure applications), stainless steel (for corrosive media), and specialized materials such as UPVC, CPVC, and polytetrafluoroethylene.
VIII. Example Selection Process
Scenario: Transporting a corrosive liquid (pH = 2), pressure 1.0 MPa, temperature 80°C, and flow rate 100 m³/h. Step 1. For corrosive liquids, select a stainless steel body (such as SUS316L). 2. For high-pressure applications, select a triple-eccentric metal-sealed butterfly valve. 3. Calculate the flow rate: Assuming a DN200 pipe diameter, the flow rate is approximately 3.5 m/s (which meets the requirements).
