What are the requirements for sealing technology of medium and high pressure valves?

The sealing technology of medium and high pressure valves is a key factor to ensure the normal operation of valves under high pressure environment and avoid leakage. Since medium and high pressure valves are often used to withstand high pressure and temperature, the quality of sealing performance directly affects the safety, stability and efficiency of the system. The following are the sealing technology requirements of medium and high pressure valves:

1. Sealing performance requirements
Prevent leakage: Sealing is one of the core elements of valve design. The sealing system of medium and high pressure valves must be able to effectively prevent the leakage of media such as gas, liquid or steam. The sealing surface must be precisely machined to ensure good contact and avoid leakage during operation.
High pressure resistance: The sealing technology must be able to withstand the high pressure environment required for the valve to work. Under high pressure, the contact pressure between the seal and the sealing surface will increase, so the sealing material is required to have high strength and pressure resistance.
High temperature resistance: Many medium and high pressure valves work in high temperature environments, and the sealing material must have good high temperature resistance to avoid softening, aging or failure under high temperature conditions. For high temperature environments, metal seals or high temperature resistant polymer seals are often used.
Corrosion resistance: Medium and high pressure valves are often used in chemical, petroleum, natural gas and other industries, with a wide variety of media and strong corrosiveness. Therefore, the sealing material and sealing surface should have good corrosion resistance and be able to cope with various corrosive media.

2. Sealing structure design requirements
Double sealing structure: In order to improve safety, many medium and high pressure valves adopt a double sealing design. For example, the design of combining metal seals with soft seals can ensure that even if the soft seals age or fail, the metal seals can still maintain the basic sealing function of the valve.
Automatic sealing design: In some valves (such as ball valves and butterfly valves), the sealing surface design has a self-sealing function. When the valve is closed, the valve seat will automatically press against the valve core or ball to enhance the sealing effect. This design can prevent external leakage and enhance the reliability of the seal.
Sealing surface surface treatment: The sealing surface of the valve is usually required to have a high-precision surface finish to avoid leakage due to a rough surface. For metal sealing valves, the sealing surface may be hardened, polished, coated and other technologies to enhance wear resistance and sealing performance.

3. Selection of sealing materials
Metal seals: Metal seals are suitable for working environments with high temperature, high pressure and corrosive media, and are often used in medium and high pressure valves such as ball valves, gate valves, and stop valves. Metal seals have the characteristics of high pressure resistance, temperature resistance, and corrosion resistance. Commonly used metal materials include stainless steel, alloy steel, and hard alloy.
Non-metallic seals: Soft sealing materials are usually used at normal temperature and pressure, have good flexibility and elasticity, and can adapt to slight deformation. Commonly used non-metallic sealing materials include polytetrafluoroethylene (PTFE), rubber, graphite, etc. In medium and high pressure valves, soft seals are usually combined with metal seals to improve the sealing effect.
Composite sealing materials: Composite materials (such as metal and non-metallic composite materials) are often used in sealing designs for special working conditions. For example, composite sealing materials with metal shells and graphite and polytetrafluoroethylene (PTFE) liners have good high temperature resistance, corrosion resistance, and pressure resistance.

4. Sealing surface design requirements
Contact surface pressure of the sealing surface: The sealing surface design of medium and high pressure valves must ensure that the sealing surface can withstand a large contact pressure. In high-pressure systems, the contact pressure of the sealing surface is usually large, so the sealing material and design are required to maintain an effective sealing effect under high pressure environments.
Shape and structure of the sealing surface: The sealing surface should be finely processed, and the shape design usually includes flat seal, conical seal, spherical seal, etc. Sealing surfaces of different shapes are suitable for different working conditions. For example, the sealing surface of a ball valve is often spherical, which is convenient for realizing the self-sealing function, while gate valves and stop valves often use flat sealing surfaces.
Accuracy requirements of the sealing surface: The accuracy of the sealing surface directly affects the sealing performance of the valve. The sealing surface is usually required to achieve high-precision processing to avoid leakage due to slight processing errors under high pressure conditions. Therefore, the sealing surface usually needs to be processed by high-precision grinding, polishing, etc.

5. Requirements for tightening and adjustment of valves
Control of sealing pressure: The sealing performance of the valve is not only related to the sealing material and the sealing surface, but also closely related to the pressure between the sealing surfaces. In order to maintain good sealing performance, the sealing pressure of the valve usually needs to be accurately controlled by fasteners such as bolts and nuts. For medium and high pressure valves, the torque of the tightening bolts needs to be evenly adjusted as required to avoid leakage caused by uneven force on the sealing surface.
Automatic sealing pressure regulation: Some valves (such as automatic regulating valves) use springs or pneumatic devices to automatically adjust the sealing surface pressure to ensure the sealing effect of the valve under different working conditions. For these valves, the adaptability of the sealing pressure is very important to adapt to different working conditions.

6. Special sealing technical requirements
Dynamic sealing: In medium and high pressure valves, some valves (such as ball valves, butterfly valves, etc.) will move frequently during operation, requiring the seal to still work effectively under dynamic conditions. Dynamic sealing design needs to take into account factors such as friction, wear, and self-lubrication of sealing materials.
Gas tightness and liquid tightness: Medium and high pressure valves need to ensure extremely high gas tightness and liquid tightness in some applications. For example, in high-demand occasions such as chemical reactions and oil and gas transportation, the gas tightness (such as preventing gas leakage) and liquid tightness (such as preventing liquid leakage) of the valve must meet strict standards.
Structural design to prevent leakage: Some special designs (such as double seals, embedded seals, back pressure seals, etc.) help maintain safety when leakage occurs. For example, some valves use a two-layer sealing structure. When the outer layer leaks, the inner layer seal can still ensure the safety of the system.

Summary
The sealing technology of medium and high pressure valves involves sealing performance, sealing materials, sealing surface design, fastening and adjustment technology, etc. The requirements of sealing technology are mainly reflected in the ability to prevent leakage, withstand high pressure, high temperature and corrosive media, and the stability of the sealing system. Selecting appropriate sealing materials and structural design, accurately controlling the sealing pressure, and regularly maintaining the sealing performance are the key to ensuring the safe and stable operation of medium and high pressure valves under high pressure environments.