Because the seal plays the role of truncation and connection, adjustment and distribution, separation and mixing of the medium on the valve channel, the sealing surface is often corroded, eroded and worn by the medium, and is very easy to damage. 

 There are two reasons for the damage of the sealing surface: man-made damage and natural damage. Man-made damage is caused by factors such as poor design, poor manufacturing, improper material selection, improper installation, poor use and poor maintenance. Natural damage is the wear and tear of the valve under normal working conditions, and the damage caused by the inevitable corrosion and erosion of the sealing surface by the medium. 

 The reasons for the damage to the sealing surface can be summarized as follows 

 1. The processing quality of the sealing surface is not good 

 It is mainly manifested in defects such as cracks, pores and clamps on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor operation in the process of overlay welding and heat treatment. The hardness of the sealing surface is too high or too low, which is caused by improper material selection or improper heat treatment. The hardness of the sealing surface is uneven and corrosion-resistant, mainly Due to the blowing of the bottom metal up during the overlay welding process, it is caused by the dilution of the alloy composition of the sealing surface. Of course, there are also design problems here. 

 2. Damage caused by improper selection and poor operation 

 The main manifestation is that the valve is not selected according to the working conditions, and the cut-off valve is used as a throttle valve, resulting in excessive pressure of the closing ratio and closing too fast or not closing tightly, causing the sealing surface to be eroded and worn. 

 Incorrect installation and poor maintenance caused the sealing surface to work abnormally, and the valve operated with disease, which damaged the sealing surface prematurely. 

 3. Chemical corrosion of the medium 

 The medium around the sealing surface does not generate electric current, and the medium directly chemically interacts with the sealing surface and corrodes the sealing surface. Electrochemical corrosion, the contact between the sealing surface, the contact between the sealing surface and the closing body and the valve body, as well as the difference in the concentration of the medium, the difference in oxygen concentration and other reasons will produce potential differences and electrochemical corrosion, resulting in the corrosion of the sealing surface of the anode side. 

 4. Erosion of the medium 

 It is the result of the wear, washing and vapor erosion of the sealing surface when the medium flows. At a certain speed, the plankton fine particles in the medium collide with the sealing surface, causing local damage. The high-speed flowing medium directly flushes the sealing surface, causing local damage. When the medium is mixed and partially vaporized, bubbles burst and impact the surface of the sealed surface, causing local damage. The erosion of the medium and the alternating effect of chemical corrosion will strongly erode the sealing surface. 

 5. Mechanical damage 

 The sealing surface will cause scratches, bruises, squeezes and other damage when opened and closed. Between the two sealed surfaces, atoms penetrate each other under the action of high temperature and high pressure, resulting in adhesion. When the two sealing surfaces move to each other, the adhesion is easy to tear. The higher the surface roughness of the sealed surface, the more likely this phenomenon is to occur. The valve will bruise and squeeze the sealing surface during the closing process and the valve flap returning to the seat, causing partial wear or indentation on the sealing surface. 

 6. Fatigue damage 

 In long-term use, the sealing surface causes fatigue on the sealing surface under the action of alternating load, resulting in cracks and peeling layers. After long-term use, rubber and plastic are prone to aging, resulting in poor performance. 

 From the above analysis of the reasons for the damage of the sealing surface, it can be seen that in order to improve the quality and service life of the valve sealing surface, it is necessary to choose the appropriate sealing surface material, reasonable sealing structure and processing method.