Optimization of High-Temperature Valve Stem Packing Sealing

In modern industrial production, valves, as key devices for controlling fluid flow, directly affect the safety, stability, and efficiency of the production process. Among them, high-temperature valves face more severe challenges due to their special working environment. In particular, the stem packing sealing technology of high-temperature valves has been a long-standing problem in the industry and is also one of the weak points in improving valve stability. This article will delve into the current status and existing problems of high-temperature valve stem packing sealing technology, and introduce an innovative compensating packing sealing structure, aiming to provide an effective solution for improving the sealing performance of high-temperature valves.

High-temperature valves, as key equipment in industrial production, have their sealing technology directly related to production safety and efficiency. Especially in high-temperature environments, stem packing sealing technology has always been a key challenge in the industry. To better understand this issue, we first need to gain a deep understanding of the definition and importance of high-temperature valves.

High-temperature valves refer to valves with an operating temperature exceeding 250℃. Under high-temperature conditions, the sealing performance of valves is put to a severe test. Stem packing sealing is a common sealing method in high-temperature valves, and its basic principle is to prevent medium leakage by contacting the packing with the stem. However, traditional stem packing sealing has many problems in practical applications, such as insufficient or excessive sealing, which leads to leakage at the valve stem after long-term operation. This leakage can not only cause equipment shutdown and property loss but may also trigger environmental pollution and safety accidents, bringing great risks to the operation of the equipment.

The sealing characteristics of valves are an important indicator for measuring valve quality. At present, most control valves and general-purpose valves use contact sealing for the stem and packing, which is widely used due to its compact structure, convenient installation and replacement, and low cost. However, this sealing method has obvious shortcomings under high-temperature conditions. The sealing effect between the packing and the stem is affected by various factors, such as the material, structure, installation method of the packing, and the working environment.

There are mainly two principles of packing sealing: bearing effect and labyrinth effect. The bearing effect refers to the formation of a boundary layer on the stem surface through the compression of the packing and the action of external lubricating fluid between the packing and the stem, creating a relationship similar to that between bearings, thereby reducing friction and maintaining a sealed state. The labyrinth effect is due to the fact that the surface flatness of the stem cannot reach an ideal level, and the packing can only partially fit with the stem, resulting in small gaps. These gaps form a labyrinth band through the staggered installation of the packing, and the medium undergoes multiple throttling and pressure reduction in it to achieve a sealing effect. However, the surface flatness of the stem and the small gaps between the packing and the stem, which the labyrinth effect relies on, objectively exist and are difficult to eliminate, which is also the root cause of leakage.

In the sealing design of high-temperature valves, choosing the right packing material is the key to ensuring sealing performance. Different working conditions put forward different requirements for the performance of packing materials, so it is necessary to select the most suitable packing material according to the specific application scenario. The following will introduce in detail several common high-temperature packing materials and their characteristics.

Common packing materials include PTFE packing, expanded graphite packing, and reinforced graphite packing. PTFE packing is mainly made of PTFE dispersion resin and has the characteristics of no additives, high cleanliness, and strong corrosion resistance. It is suitable for valves and pumps in food, pharmaceutical, papermaking industries, and those handling highly corrosive media. Its application environment temperature does not exceed 260℃, the working pressure does not exceed 20MPa, and the pH value range is 0 - 14.

Expanded graphite packing, also known as flexible graphite packing, is woven from flexible graphite yarn and has good self-lubrication, thermal conductivity, low friction resistance, strong practicability, good flexibility, and high strength, providing a cushioning effect on the shaft. Its application environment temperature does not exceed 600℃, the working pressure does not exceed 20MPa, and the pH value range is 0 - 14.

Reinforced graphite packing is based on expanded graphite packing and reinforced with materials such as glass fiber, copper wire, stainless steel wire, and nickel wire. It has all the characteristics of expanded graphite and is also a highly effective sealing element for solving high-temperature and high-pressure sealing problems, with strong practicability, good flexibility, and high strength. Its application environment temperature does not exceed 550℃, the working pressure does not exceed 32MPa, and the pH value range is 0 - 14.

In addition to the above common packing materials, there are other types of packing materials developed for special working conditions in actual production, such as aramid fiber packing with excellent chemical resistance; and aramid fiber and carbon fiber interwoven packing suitable for long-term load-rotating shafts. These special packing materials can meet the sealing requirements under specific working conditions and further expand the application range of packing sealing.

Despite the use of various packing materials in the sealing design of high-temperature valves, traditional stem packing sealing still faces many challenges in practical applications. These problems not only affect the sealing performance of the valve but may also lead to serious safety hazards and economic losses. The following are common problems and their cause analysis of high-temperature valve stem packing sealing in actual operation.

Although there are various packing materials available, traditional stem packing sealing still has many problems under high-temperature conditions. Taking graphite packing as an example, leakage is prone to occur under high-temperature conditions.

Firstly, after the graphite packing is loaded into the packing box, axial pressure is applied through the tightening screws on the packing gland. Since the packing has certain elasticity, it will undergo axial deformation and slight displacement under the action of axial pressure, closely fitting with the stem. However, this fit is not uniform, resulting in uneven medium pressure on the upper and lower packing in the packing box, and inconsistent plastic deformation of the packing, which easily leads to partial excessive or insufficient sealing between the packing and the stem.

Secondly, the packing near the gland is subjected to a larger axial clamping force and generates a greater friction force, making the stem and packing more prone to damage at this location. Moreover, under high-temperature conditions, the expansion of graphite packing increases, and so does the friction force. If the heat generated by high temperature cannot be dissipated in time, it will accelerate the wear of the stem and packing, which is also an important reason for the leakage of packing in high-temperature valves.

In response to the problems of high-temperature valve stem packing sealing, a compensating valve packing sealing structure has emerged. Different types of high-temperature packing structures have been designed for high-temperature low-pressure and high-temperature high-pressure working conditions, effectively solving the problem of easy leakage of valves under high-temperature conditions.

The high-temperature low-pressure packing sealing structure uses a specially made compensating coiled torsion spring closely combined with a composite graphite packing. Since the working pressure is not high, the packing spacer is eliminated, and a specially made compensating coiled torsion spring is added at the bottom of the packing box. During assembly, a certain preload is applied through the tightening screws. Even if friction and wear occur between the high-purity graphite packing and the stem, the coiled torsion spring can make corresponding compensating adjustments in time to ensure that the valve does not leak. The design of this structure cleverly utilizes the elastic compensating characteristics of the torsion spring, making up for the shortcomings of traditional packing sealing that is prone to leakage under high-temperature low-pressure conditions, and improving the sealing reliability and stability of the valve under high-temperature low-pressure working conditions.

The high-temperature high-pressure packing sealing structure is a cutting-edge packing system that uses a double-compensation structure with an external connection of a butterfly spring and a coiled torsion spring. This structure can effectively avoid the problem of torsion spring failure due to excessively high temperatures. Especially under the harsh conditions of high temperature and high pressure, even if one compensation point fails, the other remains effective, with the two not interfering with each other, compensating independently but simultaneously acting on the packing. The closed design of the butterfly spring also helps in use under extreme outdoor conditions, and the external connection of the two compensation points facilitates replacement without the need to disassemble the entire packing box, greatly improving the efficiency and convenience of operation. After long-term customer feedback, this packing sealing structure has shown significant effects in preventing stem leakage under high-temperature high-pressure conditions and has the characteristics of being sturdy and durable.

The stem packing sealing technology of high-temperature valves has always been a difficult problem in the industry. Traditional packing sealing methods have many shortcomings under high-temperature conditions, which are prone to leakage and other problems. The compensating valve packing sealing structure provides an effective solution to this problem. This structure, through innovative design, uses a compensation mechanism to make up for the deficiencies of traditional packing sealing and improves the sealing performance and stability of valves under high-temperature conditions. Its good performance under both high-temperature low-pressure and high-temperature high-pressure conditions demonstrates a broad application prospect.