Gate valves and globe valves are required to have upper sealing devices, mainly based on the following considerations:

1、 Prevent medium leakage and protect the filling material

Prevent medium leakage: When the gate valve and globe valve are closed, the valve stem is in a stationary position. If there is no upper sealing device, the medium may penetrate upwards along the gap between the valve stem and the valve body, causing the medium to leak out. The upper sealing device can effectively prevent medium leakage, ensuring the working performance and safety of the valve.

Packing protection: The packing box is usually sealed with flexible materials such as asbestos, polytetrafluoroethylene, etc., which are prone to corrosion, aging, and damage from long-term contact with the medium. The upper sealing device can prevent the medium from entering the packing box, protect the packing, and extend the service life of the packing.

2、 Environmental safety and energy conservation

Environmental safety: For some toxic, harmful, flammable, explosive or valuable media, preventing their 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 medium leakage at the first line of defense, which is the fit between the valve stem and the valve body, providing reliable guarantee for the sealing of the valve.

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

3、 Easy for valve maintenance and packing replacement

Online replacement of packing: 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 first to balance the pressure on both sides of the valve before operation can be carried out. This can lead to production interruptions and significant economic losses in some continuous production processes. With the upper sealing device, when replacing the packing, simply close the valve and the upper sealing device can form a seal at the valve stem to prevent medium leakage. There is no need to empty the medium in the pipeline, and online packing replacement can be achieved, greatly improving maintenance efficiency and reducing production downtime.

Convenient inspection and maintenance of valve stem: The presence of the upper sealing device allows for daily inspection, lubrication, or maintenance of the valve stem without worrying about medium leakage issues. Maintenance personnel can operate the valve stem more conveniently, perform necessary inspections and maintenance work, and ensure the normal operation of the valve stem.

4、 Improve valve reliability

Double sealing guarantee: The upper sealing device and the main seal of the valve (such as the seal between the gate and the valve seat) together form a double sealing structure. When there is a slight leakage of the main seal due to wear, impurities, or blockage, the upper sealing device can serve as a supplementary sealing defense line, continuing to ensure the sealing performance of the valve to a certain extent and improving the overall sealing reliability of the valve.

5、 Adapt to changes in working conditions

Adaptability to operating conditions: In some operating conditions, valves may be affected by frequent fluctuations in temperature, pressure, and other parameters, or may experience component deformation after long-term operation. The upper sealing device can adapt to these changes to a certain extent, maintaining a good sealing state through its own elastic deformation or fine-tuning, ensuring the stable operation of the valve under different working conditions.

6、 Compliant with standard specifications

Industry standard requirements: In the relevant standards and specifications for valve design and manufacturing, such as API 600, GB/T 12234, etc., it is clearly stipulated that gate valves and globe valves should be equipped with upper sealing devices. This is a common requirement in the industry and an important guarantee for ensuring valve quality and performance.

In summary, the requirement for upper sealing devices for gate valves and globe valves is to ensure the sealing performance of the valve, protect the packing, ensure environmental safety, facilitate valve maintenance and packing replacement, improve valve reliability, and adapt to changes in operating conditions.