In order to achieve zero leakage of internal and external seals of the valve, save energy, protect the environment and improve work efficiency, the valve must have reliable sealing performance. The sealing parts of the valve mainly include the contact between the opening and closing parts and the two sealing surfaces of the valve seat, the contact between the valve stem and the bonnet, the valve stem seal, and the gasket contact between the valve body and the bonnet. Among them, the leakage between the two sealing surfaces of the gate and the valve seat is called the internal leakage of the valve, while the leakage between the valve stem and the valve cover, the valve stem seal and the sealing surface of the valve body and the valve cover is called the external leakage of the valve. The internal leakage of the valve will affect the ability of the valve to cut off the medium. The leakage of the valve will cause the loss of the transmission medium or pollution of the environment, and even cause major accidents in serious cases. For flammable, explosive, toxic or radioactive media, leakage of valves is not allowed. In view of the problems of conical and spherical upper sealing surfaces and based on the performance analysis of the actual working conditions of the valve, the principle of plane sealing of the stop valve disc is adopted in the design of the valve upper sealing, and the original conical upper sealing surface of the valve stem and bonnet is improved to the plane contact mode. The plane contact seal between the valve stem and the valve cover is generally not affected by the equipment accuracy, tooling accuracy and the shape and position tolerance of the mating parts. It is simple in structure and easy to process. The sealing part of the valve cover can meet the design requirements only by finishing turning after surfacing. After finishing the valve stem, the valve stem head is heated to the quenching temperature and air cooled to room temperature. After finishing the sealing plane, assembly can be carried out. The first pass rate of the sealing test on the valve can reach 100%, and its service life can be the same as the opening and closing times of the valve, and the maintenance is convenient.
For stainless steel valves, the materials of the valve stem and the bonnet are generally the same austenitic material, and the two tend to adhere after pressure contact. The bonnet shall not adopt the upper sealing form of conical surface as much as possible. The sealing hole can be machined at the lower part of the packing hole of the valve cover, and the conical surface of the valve rod and the PTFE conical surface gasket are used as the sealing pairs. This structure is very suitable for the application on the pipeline with corrosive medium.
When opening the valve, the opening and closing parts shall act in place to make the upper seal play its proper function. However, it should be noted that the force should be light and moderate, not too large and too fast, so as to avoid scratching the sealing surface, prolong the service life of the valve seal, and eliminate the harm caused by the valve leakage. Practice has proved that compared with the conical sealing form, the plane sealing design of the valve has relatively low requirements for machining equipment and process equipment. Whether it is small-scale operation or batch production, it can reduce production costs and improve work efficiency, which has positive significance for stabilizing product quality and ensuring the safe operation of supporting facilities.