The sealing performance of the seal on the valve is an important technical indicator to measure the quality of the valve. The national standard has formulated relevant regulations for the technical requirements of the seal on the steel gate valve and the steel globe valve. The sealing effect of the steel gate valve and globe valve is related to the material of the valve, processing equipment, tooling manufacturing, heat treatment, processing technology, geometric tolerance and machining accuracy of parts, etc., and a certain technology does not meet the design requirements. It will directly affect the effect of the upper seal (the upper seal of the valve is shown in parts 3 to 4 in Figure 1). According to the relevant standards, the seal on the valve should have a conical or spherical sealing structure. However, the conical or spherical sealing structure has certain disadvantages compared to the flat sealing structure, such as friction on the sealing surface, difficult maintenance, high processing difficulty, and increased production costs. As a result, production costs have risen and products have become uncompetitive. At the same time, the upper sealing performance of the valve is also difficult to meet the standard technical requirements, and the upper sealing often fails after several sealing performance tests.
In view of the problems existing in the conical and spherical upper sealing surfaces and the performance analysis according to the actual working conditions of the valve, the principle of the plane sealing of the globe valve disc is adopted in the design of the upper sealing of the valve. The upper sealing surface is improved to a flat contact mode. The plane contact seal between the valve stem and the bonnet is generally not affected by the equipment accuracy, tooling accuracy and the shape and position tolerance of the matching parts, the structure is simple, and the processing is easy. After the stem is finished, the stem head is heated to the quenching temperature, air-cooled to room temperature, and can be assembled after finishing the sealing plane. The one-time pass rate of the sealing test on the valve can reach 100%, its service life can also be achieved the same as the valve opening and closing times, and it is more convenient to maintain.
Because the material of the valve stem and the valve cover is generally the same austenitic material, the stainless steel valve tends to stick after contacting under pressure, and the valve cover should not adopt the upper sealing form of the cone 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 cone surface on the valve stem and the PTFE cone surface sealing gasket are used as the sealing pair. This structure is very suitable for the pipeline with corrosive medium.
When opening the valve, the opening and closing parts should move in place, so that the upper seal can perform its due function. However, it is worth noting that the force should be light and moderate, and it should not be too large or too fast, so as not to scratch the sealing surface, prolong the service life of the seal on the valve, and prevent the harm caused by the leakage of the valve. Practice has proved that compared with the conical sealing form, the upper seal of the valve has relatively lower requirements on mechanical processing equipment and process equipment. Whether it is small-scale operation or mass production, the production cost can be reduced. Improving work efficiency has positive significance for stabilizing product quality and ensuring the safe operation of supporting facilities.