Globe valve disc plane cone problem

The opening and closing part of the globe valve (stopvalve, GlobeValve) is a plug-shaped valve disc, the sealing surface is flat or conical, and the valve disc moves linearly along the center line of the fluid. The movement form of the valve stem includes the lifting rod type (the valve stem rises and falls, the handwheel does not rise and fall), and the lifting and rotating rod type (the handwheel and the valve stem rotate and rise together, and the nut is set on the valve body). The stop valve is only suitable for fully opening and fully closing, and adjustment and throttling are not allowed. The above is the definition of a general stop valve! There are many structural designs, and their sealing principles and sealing forces are also different. Basically it is also divided into: Flat seal, cone seal, spherical seal and diameter seal. 1. The advantage of the flat seal is that there is no friction when the contact surface is close, so the guidance requirements for the closing member are not important, and the requirements for the scratch resistance of the sealing surface material are not strict. At the same time, when the roundness of the sealing surface is deformed due to pipe stress, it will not affect the sealing performance of the sealing surface. The disadvantage is that solid particles and sediments in the medium can easily damage the sealing surface. The sealing principle is that when the medium flows in from below the valve disc, the sealing force applied must be equal to or greater than the sum of the necessary specific pressure generated on the sealing surface and the upward force of the medium. When the medium flows in from above the valve disc, the sealing force applied must be equal to or greater than the difference between the required specific pressure generated on the sealing surface and the force of the medium. 2. Conical surface sealing is to make the sealing surface tapered to narrow the contact surface. Under the action of a certain sealing force, this kind of seal has a specific sealing pressure of * * Increase, the density is easy to achieve sealing. On the premise of ensuring sealing, the sealing force exerted is smaller than that of flat sealing. Since the narrow sealing surface makes it difficult for the valve disc to land correctly on the valve seat, in order to achieve the best sealing performance, the valve disc must be guided. After the valve disc is guided, better sealing performance can be achieved. When the valve disc is guided in the valve body, the lateral thrust of the flowing medium on the valve disc is borne by the valve body instead of the valve stem, which further enhances the sealing performance and the reliability of the packing seal. Conical seals are fitted under friction, so the sealing material must be resistant to scratches. Compared with flat seals, cone seals are less damaged by solid particles and media sediments, but they are not suitable for use in media containing solid particles and media sediments. Such seals are mainly used in media without particles. The sealing principle is that when the medium flows in from below the valve disc, the sealing force applied must be equal to or slightly greater than the sum of the must-specific pressure generated on the sealing surface and the upward force of the medium. When the medium flows in from above the valve disc, the sealing force applied must be equal to or greater than the difference between the must-specific pressure generated on the sealing surface and the force of the medium. In order to improve the strength of the cone seal without sacrificing its sealing stress, the cone half angle of the sealing surface is made to 15°, which provides a wider sealing surface and allows the valve disc to seal more easily with the valve seat. In order to achieve higher sealing stress, the portion of the valve seat sealing surface that contacts the valve disc is narrow, about 3mm, and the remaining tapered portion can be slightly longer. When the sealing load increases, the valve disc slides deeper into the valve seat, thereby increasing the sealing surface width. This sealing surface design is not as susceptible to erosion damage as narrow sealing surfaces. In addition, the throttling characteristics of the valve are improved due to the longer tapered surface. 3. Spherical sealing is to make the valve disc into a spherical shape and the valve seat into a tapered shape. The ball of the valve disc can rotate freely in the hole of the valve stem. Therefore, the valve disc can be adjusted by rotating within a certain range on the valve seat. Since the contact between the two sealing surfaces is almost in line, that is, line sealing, the sealing stress is very high and the sealing is easy. And because the valve disc ball can be made of carbide or ceramic materials, the hardness can reach 40-60HRC, and it can withstand very high temperatures. Therefore, it can be used as a high temperature stop valve. The disadvantage is that the linear contact of the sealing surface is easily damaged by erosion. Therefore, the valve seat should be made of erosion-resistant material. Spherically sealed stop valves are suitable for gases or liquids containing tiny solid particles in the medium. The sealing principle is that when the medium flows from below the valve disc, the sealing force applied must be equal to or slightly greater than the sum of the specific pressure generated on the sealing surface and the upward force of the medium. When the medium flows in from above the valve disc, the sealing force applied must be equal to or slightly greater than the difference between the specific pressure generated on the sealing surface and the downward force of the medium. 4. Radial sealing refers to the sealing of the plunger type stop valve. Its sealing principle is: in the plunger valve, its valve disc and valve seat are designed according to the principle of the plunger. The valve disc is designed as a plunger, and the valve seat is designed as a collar. The material of the collar can be flexible graphite or polytetrafluoroethylene. The valve seat is composed of an upper collar, an isolation ring and a lower collar, and is pressed tightly with the valve cover. This is achieved by a tight fit between the plunger and collar.