Sealing is preventing leakage, so the principle of valve sealing is also studied from preventing leakage.There are two main factors that cause leakage, one is the main factor affecting the sealing performance, that is, there is a gap between the sealing pairs, and the other is the pressure difference between the two sides of the sealing pair.The principle of valve tightness is also analyzed from four aspects: liquid tightness, gas tightness, leakage channel sealing principle and valve sealing pair.
The tightness of the liquid is carried out by the viscosity and surface tension of the liquid. When the valve leaking capillary is filled with gas, surface tension may repel the liquid or introduce liquid into the capillary. This forms a tangent angle. When the tangent angle is less than 90°, the liquid will be injected into the capillary, which will cause leakage.
Leaks occur because of the different properties of the media. Experiments with different media will yield different results under the same conditions. Water, air or kerosene can be used. When the tangent angle is greater than 90°, leakage will also occur. Because it is related to the grease or wax film on the metal surface. Once the film on these surfaces is dissolved, the characteristics of the metal surface change, and the liquid that was originally repelled will wet the surface and leak. In view of the above situation, according to the Poisson formula, the purpose of preventing leakage or reducing leakage can be achieved under the condition of reducing the diameter of the capillary and the viscosity of the medium.
According to Poisson’s formula, the tightness of a gas is related to the viscosity of the gas molecules and the gas. 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 is the same as the average degree of the gas molecules, the gas molecules flow into the capillary with thermal motion.
The valve seal consists of two parts, the roughness that is spread on the wave surface and the waviness of the distance between the wave crests. Under the circumstance that most of the metal materials in our country have low elastic strain force, if the state of sealing is to be achieved, it is necessary to raise higher requirements for the compressive force of the metal material, that is, the compressive force of the material must exceed its elasticity.