Valve Bonnets: A Detailed Guide to Types and Functions

In industrial systems, valves are the core equipment for controlling fluid flow and pressure. The valve bonnet, as an important part of the valve, directly affects the system's operational efficiency and safety through its selection and design.

This article will analyze the application of valve bonnets in high-temperature, low-temperature, and sealing control scenarios in detail from the aspects of connection methods, design types, and material selection.

The Functions And Connection Methods Of Valve Bonnets

The valve bonnet is an important component connecting the valve body and the actuator, and its main functions include stabilizing the valve structure, protecting internal components, and maintaining sealing performance. Different connection methods impact the installation, maintenance, and flexibility of valve use.

Threaded connection: The valve bonnet is screwed into the valve body and sealed with sealing elements. It has low cost but limited strength, making it unsuitable for high-pressure applications.

Welded connection: The valve bonnet is welded to the valve body, forming a permanent connection. It provides high strength and sealing performance but lacks maintenance flexibility and is difficult to disassemble, making it suitable for environments with extremely high sealing requirements.

Bolted connection: This is the most commonly used valve bonnet connection method. The valve bonnet is secured to the valve body with bolts and nuts, using gaskets or sealing rings for sealing. It is particularly suitable for scenarios requiring frequent maintenance.

Applicable Valve Types

Straight-through valves (e.g., globe valves): Valve bolted connections are the mainstream design, allowing for easy disassembly and component replacement.

Rotary valves: Typically use an integrated design where the valve bonnet becomes part of the valve body.

Valve Bonnet Design Types

• Standard valve bonnet: The most common type, suitable for general working conditions.

• Extended valve bonnet: Protects the packing and stem, making it suitable for high-temperature or low-temperature special conditions.

• Cryogenic valve bonnet: Made with special materials and designs to prevent low temperatures from affecting the seals, suitable for extremely low-temperature media.

• Bellows-sealed valve bonnet: Equipped with a bellows sealing structure inside the valve bonnet, designed to achieve leak-free sealing. It is particularly suitable for toxic, volatile, or hazardous media, offering extremely reliable sealing performance.

Temperature Adaptability of Valve Bonnet Designs

Industrial valves often need to operate under extreme temperature conditions, requiring valve bonnet designs that can withstand these demanding environments. In both high-temperature and low-temperature applications, extended valve bonnets are widely used to effectively manage heat or cold.

1. Material Selection for Valve Bonnets in High-Temperature Applications

In high-temperature conditions, the valve’s seals and actuators may fail due to heat transfer. Extended valve bonnets reduce the likelihood of heat transferring to the actuators and sealing materials by increasing the bonnet’s length.

Recommended Materials: For high-temperature applications, graphite packing and stainless steel (e.g., 304 or 316L) are recommended to meet temperature resistance requirements of up to 600°C.

2. Material Selection for Valve Bonnets in Low-Temperature Applications

In low-temperature environments, liquids can vaporize upon entering the valve bonnet area, causing system instability. Extended valve bonnets create a longer temperature transition zone, ensuring that the cold liquid remains in its liquid state.

Recommended Materials: Low-temperature carbon steel or stainless steel are preferred for low-temperature applications, as they prevent brittle failure of standard carbon steel at low temperatures. Additionally, PTFE (polytetrafluoroethylene) packing is widely used for its excellent low-temperature performance.

The Role of Valve Bonnets in Leakage Control

With the increasing environmental requirements in industrial operations, higher standards for valve sealing and leakage control are being set. Valve bonnets play a critical role in this area.

1. Advantages and Limitations of Bellows Seals

Bellows seals can achieve extremely low leakage standards (e.g., 50 ppm under ISO 15848 Class A standards). However, their high cost and complex maintenance requirements limit their application. Bellows seals are mainly used in high-precision scenarios requiring minimal leakage.

2. Common Sealing Techniques

Packing Seals: V-shaped packing or self-adjusting packing can meet most leakage control needs.

Bellows Seals: These are only used when packing seals cannot meet the required leakage standards.

3. Multi-Stage Sealing Strategies

To minimize leakage risk, a stepwise sealing optimization approach can be adopted:

Start with high-quality packing seals to meet the required standards.

If packing seals are insufficient, consider using bellows seals or other higher-precision sealing methods.

Practical Recommendations for Valve Bonnet Selection

Based on the varying demands of industrial scenarios, valve bonnet selection should comprehensively consider connection methods, temperature adaptability, and sealing performance.

1. High-Temperature Applications

Use extended designs to improve heat dissipation.

Select graphite packing and high-temperature stainless steel materials, such as 316L.

2. Low-Temperature Applications

Use low-temperature-compatible materials such as low-temperature carbon steel or PTFE packing.

Ensure the formation of an insulating layer to reduce temperature transfer to the actuator after cold liquid enters the bonnet.

3. Leakage Control Applications

Prioritize packing seals, and use bellows seals when necessary.

The selection and design of bonnets is a complex engineering task that requires finding the optimal balance between connection methods, temperature adaptability, and sealing performance. Through thoughtful design, valves can not only meet the demands of extreme operating conditions but also significantly enhance system safety and operational efficiency.

If you are looking for a high-quality and reliable valve manufacturer, TFW Valve is your ideal choice. If you have any other questions, please feel free to contact us.