Since the seal cuts off and connects, regulates and distributes, and mixes media on the valve channel, the sealing surface is often corroded, eroded, and worn by the medium and is easily damaged.
There are two reasons for sealing surface damage: 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 of the valve under normal working conditions, and it is 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 inclusions on the sealing surface, which are caused by improper selection of surfacing welding and heat treatment specifications and poor operation in the process of surfacing welding and heat treatment. The hardness of the sealing surface is too high or too low, which is due to incorrect material selection. Or caused by improper heat treatment, the hardness of the sealing surface is uneven, and it is not resistant to corrosion, mainly because the underlying metal is blown to the top during the surfacing process, which dilutes the alloy composition of the sealing surface. Of course, there are also design issues here.
2. Damage caused by improper selection and poor operation.
The main performance 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 closing specific pressure and too fast or lax closing, causing erosion and wear on the sealing surface.
Improper installation and poor maintenance will cause the sealing surface to work abnormally, and the valve will run with a disease, which will damage the sealing surface prematurely.
3. Chemical corrosion of the medium.
When the medium around the sealing surface does not generate current, the medium directly reacts with the sealing surface and corrodes the sealing surface. Electrochemical corrosion, the contact between the sealing surfaces, the contact between the sealing surface and the closing body and the valve body, the concentration difference of the medium, the oxygen concentration difference, etc., will cause a potential difference and electrochemical corrosion will cause the sealing surface on the anode side to be corroded.
4. The erosion of the medium.
It is the result of wear, erosion, and cavitation of the sealing surface when the medium flows. When the medium is at a certain speed, the floating fine particles in the medium collide with the sealing surface, causing local damage. The high-speed flowing medium directly scours the sealing surface, causing local damage. When the medium is mixed and partially vaporized, air bubbles burst and impact the seal. surface, causing localized damage. The erosion of the medium and the alternating action of chemical corrosion will strongly erode the sealing surface.
5. Mechanical damage.
During the opening and closing process, the sealing surface will be damaged by scratches, bruises, squeezes, etc. Between the two sealing surfaces, atoms penetrate each other under the action of high temperature and high pressure, resulting in adhesion phenomenon. When the two sealing surfaces move relative to each other, the adhesion is easy to tear. The higher the surface roughness of the sealing surface, the more likely this phenomenon will occur. During the closing process of the valve, the valve disc will bruise and squeeze the sealing surface during the process of returning to the seat, which will cause partial wear or indentation on the sealing surface.
6. Fatigue damage.
During the long-term use of the sealing surface, under the action of alternating load, the sealing surface will be fatigued, and cracks and peeling layers will appear. Rubber and plastics are prone to aging after long-term use, resulting in poor performance.
From the above analysis of the cause of damage to 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 select appropriate sealing surface materials, reasonable sealing structures and processing methods.