Gate valves and globe valves require an upper sealing device, which is mainly based on the following considerations: 

 I. Prevention of media leakage and filler protection 

 • Prevent media leakage: When the gate valve and globe valve are closed, the stem is in a stationary position. Without an upper sealing device, the medium may penetrate upward along the gap between the stem and the valve body, causing the media to leak. The upper sealing device can effectively prevent the leakage of the medium and ensure the performance and safety of the valve. 

 • Filling protection: The packing letter is usually sealed with flexible materials such as asbestos and polytetrafluoroethylene, and long-term contact media are prone to erosion, aging and damage. The upper sealing device can prevent the medium from entering the packing letter, protect the packing and prolong the service life of the packing. 

 II. Environmental safety and energy conservation 

 • Environmental safety: For some toxic, harmful, flammable, explosive or valuable media, preventing leakage is not only a guarantee for the safety of the working environment, but also a necessary measure to avoid environmental pollution. The upper sealing device can prevent the leakage of the medium at the first line of defense, that is, the combination of the stem and the valve body, providing a reliable guarantee for the sealing of the valve. 

 • Energy saving: Preventing media leakage can also avoid waste of resources, which is in line with the environmental protection concept of energy conservation and emission reduction. 

 III. Easy valve maintenance and packing replacement 

 • Online filler replacement: When it is necessary to replace the packing, if there is no upper sealing device, the medium in the pipeline where the valve is located must be emptied to balance the pressure on both sides of the valve before operation. This will lead to the interruption of production and cause greater economic losses in some continuous production processes. With the upper sealing device, when replacing the filler, you only need to close the valve, and the upper sealing device can form a seal at the stem to prevent the leakage of the medium. There is no need to empty the medium in the pipeline, which can replace the filler online, which greatly improves the maintenance efficiency and reduces the production downtime. 

 • Convenient for stem inspection and maintenance: The existence of the upper sealing device makes it unnecessary to worry about media leakage when conducting daily inspection, lubrication or maintenance of the stem. Maintenance personnel can operate the stem more conveniently and carry out the necessary inspection and maintenance work to ensure the normal operation of the stem. 

 IV. Improve the reliability of the valve 

 • Double seal guarantee: The upper sealing device and the main seal of the valve (such as the seal between the gate plate and the seat) together form a dual seal structure. When the main seal leaks slightly due to wear and tear, impurity jams, etc., the upper sealing device can be used as a supplementary seal defense line to continue to ensure the sealing performance of the valve to a certain extent and improve the overall sealing reliability of the valve. 

 V. Adapt to changes in working conditions 

 • Adaptability of working conditions: In some working conditions, the valve may be affected by frequent fluctuations of temperature, pressure and other parameters, or deformation of components after long-term operation. The upper sealing device can adapt to these changes to a certain extent. Through its own elastic deformation or fine-tuning, it always maintains a good sealing state to ensure the stable operation of the valve under different working conditions. 

 VI. Comply with standards and norms 

 • Industry general requirements: In the relevant standards and specifications for valve design and manufacturing, such as API 600, GB/T 12234, etc., gate valves and globe valves should be equipped with upper sealing devices. This is a general requirement in the industry and an important guarantee to ensure the quality and performance of valves. 

 In summary, gate valves and globe valves require an upper sealing device to ensure the sealing performance of the valve, protect the filler, ensure environmental safety, facilitate valve maintenance and filler replacement, improve valve reliability, and adapt to changes in working conditions.