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

One. Prevention of medium leakage and protection of packing

Prevent medium leakage: When gate valves and globe valves are in the closed state, the valve stems remain at rest. If there is no upper sealing device, the medium may seep upward along the gap between the valve stem and the valve body, causing the medium to leak out. The upper sealing device can effectively prevent the leakage of the medium and ensure the working performance and safety of the valve.

Packing protection: The packing box is usually sealed with flexible materials such as asbestos and polytetrafluoroethylene. Long-term contact with the medium makes it prone to erosion, aging and damage. The upper sealing device can prevent the medium from entering the stuffing box, protecting the packing and prolonging its service life.

Two. 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 the medium from leaking at the first line of defense, namely the fit between the valve stem and the valve body, providing a reliable guarantee for the sealing of the valve.

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

Three, it is convenient for valve maintenance and packing replacement

Online packing replacement: When packing replacement is required, if there is no upper sealing device, the medium in the pipeline where the valve is located must be drained first to balance the pressure on both sides of the valve before the operation can be carried out. This can lead to production disruptions in some continuous production processes, causing significant economic losses. With the upper sealing device, when replacing the packing, only the valve needs to be closed, and the upper sealing device will form a seal at the valve stem to prevent the medium from leaking. There is no need to empty the medium in the pipeline, and the packing can be replaced online, which greatly improves the maintenance efficiency and reduces the production downtime.

The valve stem inspection and maintenance are convenient: The existence of the upper sealing device ensures that when conducting daily inspections, lubrication or maintenance on the valve stem, there is no need to worry about medium leakage. Maintenance personnel can operate the valve stem more conveniently, carry out necessary inspections and maintenance work, and ensure the normal operation of the valve stem.

Four, enhance the reliability of valves

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 the main seal has slight leakage due to wear, impurity jamming and other reasons, 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.

Five. Adapt to changes in working conditions

Working condition adaptability: In some working conditions, valves may be affected by frequent fluctuations in parameters such as temperature and pressure, or may experience component deformation 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.

Six. Comply with standards and norms

General industry 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 sealing devices. This is a common requirement in the industry and also an important guarantee for ensuring the quality and performance of valves.

In conclusion, the requirement that gate valves and globe valves be equipped with upper sealing devices is to ensure the sealing performance of the valves, protect the packing, guarantee environmental safety, facilitate valve maintenance and packing replacement, enhance valve reliability, and adapt to changes in working conditions, among other demands.