Because the seal acts as a truncation and connection, regulation and distribution, separation and mixing media in the valve passage, the seal surface is often corroded, eroded, worn, and easily damaged by the media. Sealing surface damage due to human damage and natural damage of two. Man-made damage is due to poor design, manufacturing is not refined, improper material selection, improper installation, poor use and maintenance and other factors caused. Natural damage is the valve under normal wear and tear, is the media on the sealing surface of the inevitable corrosion and erosion caused damage. Cause sealing surface damage can be summarized as follows. The sealing surface processing quality is poor, mainly in the sealing surface cracks, pores and ballast and other defects, due to improper selection of welding and heat treatment and welding and heat treatment process caused by poor operation, the sealing surface hardness is too high or Too low is due to improper material selection or heat treatment caused by uneven sealing surface hardness, corrosion resistance, mainly due to the bottom of the metal in the surfacing process to blow up to dilute the sealing surface alloy composition caused. Of course, there are also design issues. Improper selection and damage caused by improper operation. The main performance is not selected according to conditions of the valve, the cut-off valve when used as a throttle valve, resulting in close than the pressure is too large and close too lax or closed, so that the sealing surface erosion and wear. Improper installation and poor maintenance lead to the sealing surface is not working properly, the valve sick, premature damage to the sealing surface. Medium chemical corrosion, the media around the sealing surface in the absence of current circumstances, the media directly from the sealing surface chemical reaction, corrosion sealing surface. Electrochemical corrosion, the sealing surface contact with each other, the sealing surface and the closing body and valve body contact and the concentration of the media, oxygen concentration and other reasons, will have a potential difference electrochemical corrosion occurs, resulting in the anode side of the sealing surface is corroded. Erosion of the medium, which is the result of wear, erosion and cavitation of the sealing surface when the medium flows. Medium at a certain speed, the medium in the flotation of fine particles collide with the sealing surface, causing local damage, high-speed flow of medium directly washed sealing surface, causing local damage, the media mixed flow and local vaporization, the bubble blast seal generated Surface, causing localized damage. Erosion of the media combined with chemical corrosion alternating role, will be a strong erosion of the sealing surface. Mechanical damage, the sealing surface in the opening and closing we will have scratches, bumps, crushing and other damage. Between the two sealing surfaces, under the action of high temperature and high pressure atomic mutual penetration, resulting in adhesion phenomenon. When the two sealing surfaces move each other, the adhesion is easily pulled. The higher the surface roughness of the sealing surface, the more likely it is. During the closing process of the valve, the valve flap will bruise and crush the sealing surface during the process of returning to the seat, causing partial abrasion or indentation on the sealing surface. Fatigue damage, the sealing surface in the long-term use, the three refined valve under alternating load caused the sealing surface fatigue, cracks and stripping layer. Rubber and plastic after long-term use, prone to aging, leading to poor performance. From the above analysis of the sealing surface damage can be seen, to improve the quality and service life of the valve sealing surface, we must select the appropriate sealing surface material (see the material part), a reasonable sealing structure and processing methods. Three fine valves
