Sealing is to prevent leakage, so the stainless steel valve sealing principle is also for the prevention of leakage. Two main factors cause leakage, one is the main factor affecting the sealing performance, that is, there is a gap between the sealing vice, and the other is the pressure difference between the two sides of the sealing vice. The stainless steel valve sealing principle is also from the liquid sealing, gas sealing, leakage channel sealing principle, and stainless steel valve sealing vice, and the other four aspects to analyze.
1. Liquid sealing
Liquid sealing is carried out by the viscosity and surface tension of the liquid. When the stainless steel valve leaks, a capillary filled with gas, surface tension may be liquid repulsion, or the liquid may enter the capillary. This forms the angle of tangency. When the angle of tangency is less than 90°, the liquid is injected into the capillary, and a leak occurs.
The reason for the leakage is the different nature of the medium. The test with different media, under the same conditions, will give different results. You can use water, air, or kerosene, etc. Leakage can also occur when the angle of tangency is greater than 90°. This is because of the relationship with the greasy or waxy films on the metal surfaces. Once the film on these surfaces is dissolved, the properties of the metal surface change, and the liquid that was repelled from the surface becomes wet and leaks. For the above situation, according to Poisson's formula, the capillary diameter and medium viscosity can be reduced in the case of large to achieve the purpose of preventing leakage or reducing the amount of leakage.
2. The gas sealing
According to Poisson's formula, the gas seal is with the gas molecules and gas viscosity. Leakage is inversely proportional to the length of the capillary and the viscosity of the gas and proportional to the diameter of the capillary and the driving force. When the diameter of the capillary and the average degree of freedom of the gas molecules are the same, the gas molecules will flow into the capillary with free thermal movement.
Therefore, when we do the sealing test of stainless steel valves, the medium must be water to achieve the sealing effect, and air, i.e., gas, will not be able to achieve the sealing effect. Even if we reduce the diameter of the capillary tube to below the molecular level of the gas by plastic deformation, we still cannot stop the flow of gas. The reason for this is that the gas can still diffuse through the metal wall. So we must be more stringent than the liquid test when we do the gas test.
3. The sealing principle of the leakage channel
The stainless steel valve seal consists of two parts: the unevenness of the scattered waveform surface and the roughness of the corrugation degree of the distance between the crests. In our country, most of the metal material elastic strains are low; if you want to achieve a sealed state, you need to put higher requirements on the compression force of the metal material, that is, the material compression force to exceed its elasticity.
Therefore, in the design of stainless steel valves, the seal is combined with a certain hardness difference to match the effect of sealing under pressure, which will produce a certain degree of plastic deformation. If the sealing surface is all metallic material, then the surface unevenness of the projection point will appear early, in the initial need to use only a small load.
