Advanced Sealing Technology in Self-Sealing Valves

The core advantage of self-sealing valves lies in their use of medium pressure to enhance sealing performance, rather than relying solely on mechanical force. This design ensures that as the medium pressure increases, the sealing force also increases, resulting in better sealing. Compared to traditional forced-sealing valves, self-sealing valves perform exceptionally well in high-temperature and high-pressure conditions, where their sealing performance not only remains stable but may even improve. This characteristic makes self-sealing valves widely applied in high-demand fields such as petrochemicals, natural gas, aerospace, and nuclear power plants.

Today, let us delve into the core principles, applications, and differences between self-sealing valves and forced-sealing valves. Understanding these will help us better appreciate why self-sealing valves play such an important role in various industries and why they are indispensable in modern industrial systems.

The core principle of self-sealing valves can be summarized as follows: utilizing the medium's pressure to act on a specific sealing element, causing it to undergo elastic or plastic deformation. This compresses the sealing element more tightly against the sealing surface, forming a forced seal. The brilliance of this design lies in the fact that as the medium pressure increases, the compressive force on the sealing surface becomes stronger, enhancing the sealing effect. This contrasts with traditional forced-sealing valves, where the sealing performance tends to decline as the medium pressure increases.

In high-temperature conditions, the advantages of self-sealing valves become even more apparent. For forced-sealing valves, the thermal expansion of the valve stem and body leads to a decrease in sealing force, increasing the risk of leakage. However, this is not the case for self-sealing valves. On the contrary, high temperature may enhance the sealing effect of self-sealing valves, as the increased medium pressure further compresses the sealing element, ensuring a tighter seal with the sealing surface.

Now, let us explore the typical application fields of self-sealing valves, examining how they play a crucial role in ensuring the smooth operation and safety of industrial production in various complex working conditions.

The wedge gate valve is the most classic and widespread application of self-sealing valves. Its valve disc is wedge-shaped, which can be single or double wedge. Both sides have sealing surfaces, and the valve body has corresponding wedge-shaped sealing seats. When the valve is closed, a downward force is applied to the valve stem, pushing the wedge-shaped valve disc towards the valve seat. At this point, the medium pressure enters from the valve inlet and acts on the backside of the wedge-shaped valve disc, "pushing" or "forcing" it against the sealing seat at the outlet. As the medium pressure increases, this pushing force and sealing compressive force also increase, resulting in better sealing performance.

In addition to wedge gate valves, some specially designed globe valves also utilize the self-sealing principle. These globe valves have valve discs designed in a piston shape or with an elastic lip edge. When the valve closes, the medium pressure acts on the top or backside of the valve disc, forcing it to press more tightly against the valve seat. High-pressure Y-type globe valves are a typical example of this design. These valves offer more reliable sealing performance than regular globe valves, particularly in high-pressure conditions, and are widely used in high-pressure process pipelines in the petroleum and chemical industries.

In valve sealing design, preventing external leakage is just as important as preventing internal leakage. The self-sealing valve bonnet is a structure specifically designed to prevent leakage from the valve stem area (where the bonnet connects to the valve body). Unlike ordinary flat gaskets, this bonnet uses an elastic self-sealing ring, typically made of a stainless steel frame wrapped in flexible graphite. Initially, the self-sealing ring is compressed by the bonnet bolts to form a preliminary seal. When the valve is pressurized, the pressure enters the chamber behind the self-sealing ring and acts on its backside, causing it to expand outward and press more tightly against the internal walls of the valve bonnet and body, achieving the effect that "the higher the pressure, the better the seal." This design is ideal for high-temperature and high-pressure conditions, as even if the bolts elongate due to creep, reducing the preloading force, the self-sealing structure can compensate for this with internal pressure, preventing external leakage and ensuring high safety.

The valve disc of a pressure reducing valve is typically designed in a piston form, with its movement and sealing relying on the medium's own pressure for balance and adjustment, displaying the self-sealing characteristic. The structure of this type of valve mainly includes the bonnet, support ring, stop ring, sealing gasket, etc. The working principle is as follows: after the valve is installed, preloading force is applied to the connection, causing the bonnet to rise, creating a force between the bonnet and the sealing gasket, as well as between the gasket and the valve body. This force compresses the gasket to create an initial sealing condition. Once the system is in operation, as the fluid pressure increases, the force acting on the bonnet increases, causing it to move upward. This increases the sealing compressive force between the bonnet, gasket, and valve body, ensuring effective sealing. The higher the medium pressure, the greater the sealing compressive force, and the better the sealing performance. This technology is commonly used in high-pressure globe valves, high-temperature globe valves, high-pressure welded globe valves, and large-diameter valves.

Exceptional Sealing Performance: The core advantage of self-sealing valves is their excellent sealing performance. As the medium pressure increases, the sealing compressive force grows, leading to better sealing, making them perform exceptionally well in high-pressure and high-temperature conditions.

Adaptability to High-Temperature and High-Pressure Conditions: In high-temperature and high-pressure conditions, the sealing performance of self-sealing valves not only remains stable but may even improve. This contrasts with forced-sealing valves, which tend to experience a decrease in sealing compressive force and leakage issues under such conditions.

High Safety: The design of self-sealing valves ensures that they provide high safety even in high-temperature and high-pressure conditions. Even if adverse factors such as bolt creep cause a decrease in preloading force, the self-sealing structure compensates with internal pressure, preventing external leakage and ensuring safe operation.

Wide Range of Applications: Self-sealing valves are widely used in high-demand fields such as petrochemicals, natural gas, aerospace, and nuclear power plants. These fields require valves with exceptional sealing performance, safety, and reliability, and self-sealing valves, with their unique advantages, are the first choice in these industries.

Petrochemicals: In the petrochemical industry, self-sealing valves are widely used in high-pressure process pipelines, reactors, towers, and other equipment. These devices often operate under high temperature and pressure, and self-sealing valves effectively prevent medium leakage, ensuring the safety and stability of the production process.

Natural Gas: The transportation and processing of natural gas require highly reliable valves. Self-sealing valves play a critical role in natural gas pipelines, compressors, storage tanks, etc., effectively preventing gas leakage and avoiding safety incidents such as fires and explosions.

Aerospace: The aerospace sector demands extremely high reliability and safety. Self-sealing valves are widely used in critical components of aircraft engines, fuel systems, hydraulic systems, etc., ensuring the safety and reliability of flight operations.

Nuclear Power Plants: The safe operation of nuclear power plants relies on reliable valve equipment. Self-sealing valves are crucial in nuclear reactors, cooling systems, steam generators, and other equipment, effectively preventing the leakage of radioactive materials and ensuring the safe operation of the plant.

Valves primarily use two types of sealing forms: forced-sealing and self-sealing. Understanding the characteristics and appropriate application scenarios of these two sealing methods is crucial for selecting the right valve.

Forced-sealing relies on the flange bolts to apply compressive force on the sealing gasket, achieving sealing in the valve. Initially, tightening the bonnet bolts compresses the gasket, filling the gaps on the sealing surface to create initial sealing conditions. As the medium pressure rises and the valve operates, the compressive force on the sealing surface may decrease, and the gasket may rebound. If the gasket has sufficient resilience, it maintains a good seal. However, forced-sealing valves require a residual compressive force on the sealing surface to maintain sealing. Typically, forced-sealing structures, such as flat gaskets, spiral wound gaskets, and serrated gaskets, are used for middle and low-pressure valves.

In contrast to forced-sealing, self-sealing is a high-pressure sealing technology commonly used in high-temperature and high-pressure large-diameter valves. These valves typically use a wedge-shaped gasket with a self-sealing structure. Before pressurization, pre-tightening bolts create initial sealing conditions between the bonnet and the gasket. As the medium pressure rises, the bonnet moves upward, increasing the sealing compressive force and improving sealing performance.

Self-sealing valves, with their unique design and outstanding sealing performance, play a critical role in the industrial field. They effectively prevent medium leakage, ensure the safe operation of equipment, and excel in high-temperature and high-pressure conditions. Compared to traditional forced-sealing valves, self-sealing valves offer significant advantages and are widely used in high-demand fields such as petrochemicals, natural gas, aerospace, and nuclear power plants. In summary, self-sealing valves are the guardians of the industrial field, providing solid support for the development of modern industry with their exceptional performance and wide application.