Sealing is to avoid leakage, so the principle of valve sealing is also from the avoidance of leakage research. There are two main elements of the formation of leakage, one is the most important factor affecting the sealing function, that is, there is a gap between the sealing pair, the other is there is a pressure difference between the two sides of the sealing pair. The principle of valve sealing is also from the liquid sealing, gas sealing, leakage channel sealing principle and valve sealing pair and other four aspects to analyze.
1. Sealing of liquid The sealing of liquid is carried out by the viscosity and surface tension of liquid. When the leaking capillary of the valve is filled with gas, the external tension may repel the liquid or draw it into the capillary. And that forms the tangent Angle. When the tangent Angle is less than 90°, the liquid will be injected into the capillary tube, and leakage will occur. The cause of leakage lies in the different properties of the medium. Experiment with different media, under the same condition, will get different results. Can use water, air or oil. When the tangent Angle is greater than 90°, leakage will also occur. Due to the relationship with the grease or waxy film on the metal surface. Once these outer films are dissolved, the characteristics of the metal surface change, and the liquid, which is originally repelled, will penetrate the surface and leak out. In view of the above situation, according to Poisson's formula, the purpose of avoiding leakage or reducing leakage can be accomplished under the condition of reducing capillary diameter and medium viscosity.
2. Gas tightness According to Poisson formula, gas tightness is related to the viscosity of gas molecules and gases. 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 freedom of the gas molecules are the same, the gas molecules will flow into the capillary with free thermal motion. Therefore, when we do the valve sealing test, the medium must use water to seal the effect, and the air or gas can not seal the effect. Even if we reduce the capillary diameter below the gas molecule by plastic deformation method, it still cannot obstruct the gas activity. The reason is that the gas can still disperse through the metal walls. So when we do the gas test, we must be more strict than the liquid test.
