• The Sealing & Principle of Triple Eccentric Metal Seated Butterfly Valves

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The Sealing & Principle of Triple Eccentric Metal Seated Butterfly Valves

  • Feb 07, 2023
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The sealing and principle
As a control part in the pipeline, a valve plays a role in controlling and regulating the medium in the pipeline no matter what structure it is in, so there are special requirements for the sealing pair of the valve.
 
1. Sealing
The relative movement of the contact seal pair can be divided into a dynamic seal and a static seal. Generally speaking, the contact seal is relatively tight; the contact seal can be divided into two categories: elastic seal and non-elastic seal. The elastic seal is mainly made of an elastic polymer. The elastic effect of the sealing material supports the compensation of plastic deformation and can effectively avoid the gap. At the same time, it has the characteristics of a simple structure, low costs, and a good sealing effect. However, the degree of heat resistance is relatively poor the service life is short. The sealing surface of non-elastic seals is mainly made of graphite, metal and other non-elastic materials. They are used in wear compensation mechanisms and micro elastic deformation, which puts forward higher requirements for structural processing, so the cost is relatively high. It has a good heat resistance and cold resistance, which is used in high-parameter seals and has a long service life.
 
2. Sealing principles
The important goal of sealing is to avoid leakages, but the cause of leakage should be analyzed objectively, and leakages of media should be avoided through various methods. When the gap between the sealing pairs is below the molecular diameter of the fluid, it can ensure that the fluid does not leak. Generally, the gap to avoid leakage should be kept within 0.003 microns. After fine grinding, the roughness of the metal surface also exceeds 0.1 microns. Therefore, the method of improving the sealing by controlling the roughness of the sealing surface is not very operable. If the sealing specific pressure in the pipeline is increased, the microscopic peak of the sealing surface is flattened, and the gap is reduced to the situation where the fluid cannot pass, the sealing effect can be achieved.
 
3. The sealing pair of the valve
The valve sealing pair refers to the part where the valve seat and the closing member contact each other to close. During use, the metal sealing surface is susceptible to entrapped media and wear particles, and is also damaged by erosion, corrosion and cavitation. If the wear particles are rougher than the unevenness of the surface, the surface accuracy will deteriorate during the running-in period of the seal. Therefore, the size of the wear particles depends not only on the material and working conditions, but also on the lubricity of the medium and the corrosion of the sealing surface. In general, it is better to choose a material with good erosion resistance, good corrosion resistance and wear resistance for the sealing, otherwise, it cannot be applied to the sealing surface.
 
4. Conclusion
To sum up, many factors affect the sealing of valves, and they are also very complicated, mainly reflected in the following aspects:
(1) It is affected by the physical characteristics of the medium, such as temperature, humidity, hydrophilicity, etc.
(2) It is affected by the structure of the sealing surface. Because the seal is not rigid, under the action of the sealing force, coupled with the influence of the working environment, the change of the structural size will be affected, forming a gap between the sealing pairs and reducing the sealing.
(3) It is affected by sealing pair materials, mainly in its selection and matching.
(4) It is affected by the sealing-specific pressure, which is mainly determined by the pressure difference or external force between the front and back of the valve, which will have a direct impact on the sealing and reliability.