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Because the seal plays a role in cutting and connecting, adjusting and distributing, separating and mixing media on the valve channel, the sealing surface is often subjected to medium corrosion, erosion, wear and easily damaged.
The reasons for the damage of sealing surface are man-made damage and natural damage. Artificial damage, is due to the design and manufacture not jing, material selection and week, undeserved, factors such as lack of bad installation is not straight, use and maintenance. Natural damage is the wear of the valve under normal working conditions, and is the damage caused by the inevitable corrosion and erosion of the medium on the sealing surface.
Causes of the sealing surface damage, can be summarized as the following several kinds:
1. sealing surface processing quality is not good
It is mainly manifested in the defects of cracks, pores and ballast on the sealing surface, which are caused by improper selection of surfacing and heat treatment specifications and poor operation in the process of surfacing and heat treatment. The hardness of the sealing surface is too high or too low, which is caused by incorrect material selection or improper heat treatment. The hardness of the sealing surface is uneven and not resistant to corrosion, mainly due to the bottom metal blown to the top during the surfacing process. Caused by diluting the alloy composition of the sealing surface. Of course, there are design issues.
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 too large specific closing pressure and too fast or lax closing, so that the sealing surface is eroded and worn.
Improper installation and poor maintenance led to abnormal operation of the sealing surface, and the valve operated with disease, prematurely damaging the sealing surface.
3. chemical corrosion of the medium
When the medium around the sealing surface does not produce current, the medium directly acts on the sealing surface chemically and corrodes the sealing surface. Electrochemical corrosion, sealing surface contact with each other, sealing surface contact with the closing body and the valve body, as well as the concentration difference of the medium, oxygen concentration difference and other reasons, will produce potential difference, electrochemical corrosion, resulting in the anode side of the sealing surface is corroded.
4. medium erosion
It is a medium flow of sealing surface wear, erosion and cavitation. Medium under a certain speed, variety of fine particle collision seal face in medium, make its local damage, high-speed flow of medium directly scour sealing surface, make its local damage, medium mixed flow and partial vaporization, a bubble blasting impact surface of sealing surface, cause local damage. The erosion of the medium combined with the alternating action of chemical corrosion will strongly etch the sealing surface.
5. Mechanical damage
Sealing surface produces in the open and close a za bruises, bruised, against damage. Between the two sealing surfaces, atoms penetrate each other under the action of high temperature and high pressure, resulting in adhesion. When the two seal face each other while moving, adhesion in easy to tear. The higher the surface roughness of the sealing surface, the more easily this phenomenon occurs. During the closing process of the valve and the valve disc in the process of returning to the seat, the sealing surface will be hurt and squeezed, causing local wear or indentation on the sealing surface.
6. Fatigue damage
In the long term use of the sealing surface, under the action of alternating load, the sealing surface will produce fatigue, crack and stripping layer. Rubber and plastic after long-term use, easy to produce aging phenomenon, resulting in poor performance.
You can see from the above analysis of the sealing surface damage reason, to improve the quality of the valve sealing surface and the service life, must choose proper sealing surface material, the reasonable structure of sealing and the processing method.