Optimize Sealing Structure of High-Performance Butterfly Valve

High-performance butterfly valves are crucial components in industrial applications. Since the mid-1960s, their design and application have significantly advanced with the introduction of PTFE as a seat material. These butterfly valves are known for their excellent sealing capabilities and versatility, making them suitable for high-pressure, high-temperature, and corrosive media in various piping systems. This article provides a comprehensive analysis of the sealing structure, material selection, and optimization of high-performance butterfly valves to ensure their reliability and long-term performance.

Overview of Sealing Structures

 
High-performance butterfly valves typically use a double-eccentric and spherical sealing structure. This design enhances the valve's sealing performance and extends its lifespan. The key components include the butterfly plate, sealing ring, and valve seat. The material and design of the sealing ring directly impact the valve's performance.

1. Double-Eccentric Design

 
The double-eccentric design involves the rotation axis of the valve plate being offset from the centerline of the valve body, and the center of rotation of the butterfly plate is not aligned with the sealing surface. This design ensures that the sealing surface contacts the valve seat more evenly when the valve is closed, reducing friction and improving sealing effectiveness.

2. Spherical Sealing Structure

 
The spherical sealing structure features a spherical-shaped inner surface of the sealing ring, which forms a good seal when in contact with the butterfly plate. This structure maintains stable sealing performance under high pressure and temperature conditions and is suitable for various media, including corrosive ones.

Sealing Ring Materials and Performance

 
The choice and performance of sealing ring materials are crucial for ensuring the efficient and reliable operation of high-performance butterfly valves. The material and design of the sealing ring significantly affect the valve's sealing effectiveness, durability, and overall performance.

1. Advantages of Polytetrafluoroethylene (PTFE)

 
PTFE is a commonly used sealing ring material in high-performance butterfly valves. Its advantages include:
 
Wide Temperature Range: PTFE can operate stably within a range of -100°C to +260°C.
Excellent Corrosion Resistance: PTFE resists most chemicals and corrosive media effectively.
Low Friction Coefficient: Reduces the torque required for valve operation, enhancing service life.
However, PTFE has some drawbacks:
 
Low Mechanical Strength: In high-pressure applications, material deformation may occur.
Poor Wear Resistance: Long-term use may lead to sealing ring wear.
"Cold Flow Tendency": Under prolonged load, PTFE can undergo permanent deformation, similar to the yield phenomenon in plastic materials.

2. Optimization of Sealing Ring Design

 
To overcome the limitations of PTFE, the sealing ring design should address the following aspects:
 
Strict Adherence to Pressure-Temperature Ratings: Ensure the sealing ring operates within specified pressure and temperature ranges.
Use of Filled PTFE: Fillers can enhance the mechanical strength and wear resistance of PTFE.
Design of Appropriate Sealing Structures: The sealing ring should be designed to leverage media pressure for sealing, ensuring it can deform in the opposite direction to prevent leakage when media flows backward.

Practical Application of Sealing Structures

 
The design of sealing structures must not only meet theoretical performance requirements but also demonstrate reliability and stability in practical applications. Here's how sealing structures perform in high-performance butterfly valves:

1. Interaction Between Butterfly Plate and Sealing Ring

When there is no media pressure, the torque transmitted by the valve stem creates sufficient sealing compression between the butterfly plate and the sealing ring. With media pressure, the sealing ring is pressed tightly against the sealing surface of the butterfly plate, further enhancing the sealing effect. During reverse media flow, the sealing ring deforms in the opposite direction, creating sealing compression to prevent leakage.

2. Design and Fixing of Protectors

The design of the protector and its screws must ensure they can withstand the maximum pressure differential rating when the end flanges are removed. The load on the protector screws should be checked based on ambient temperature conditions, as PTFE sealing rings are used at temperatures not exceeding 200°C. The protector should be designed with sufficient strength and pressure resistance to ensure the valve's safety and reliability in actual operating conditions.

Torque Control and Optimization

 
In high-performance butterfly valve applications, torque control and optimization are crucial for enhancing valve performance and ensuring reliability.

1. Causes of Torque Discrepancies

 
The actual torque of the valve may differ from the calculated torque, especially for sizes NPS12 and above. This discrepancy is primarily due to insufficient processing accuracy and surface finish of the valve stem, sealing ring, or butterfly plate, low concentricity between the valve stem and body bore, or uneven bolt pre-torque of the packing gland.

2. Optimization Measures

 
To improve valve performance, the following measures should be taken:
 
Enhance Processing Techniques: Improve the accuracy and surface finish of components.
Control Surface Roughness: Ensure the surface roughness of the contact area between the stem and packing is very smooth, while maintaining moderate smoothness for the packing box.
Optimize Sealing Ring and Butterfly Plate Processing: Ensure the concentricity of the valve body and stem mating surfaces, and improve mating precision through precision machining.
 
The sealing structure design of high-performance butterfly valves is critical for ensuring reliable operation under various demanding conditions. By selecting appropriate sealing materials, optimizing sealing ring designs, improving protector and screw designs, and rigorously controlling torque, the performance and service life of the valves can be significantly enhanced. Understanding and applying these design principles will contribute to efficient and safe flow control in practical applications.