Valve sealing performance requirements, to prevent leakage Angle. According to the different parts and degrees of leakage, resulting in different leakage of valves, therefore, different leakage prevention measures need to be put forward.

Principle of valve sealing

Sealing is to prevent leakage, so the principle of valve sealing is also from preventing leakage research. There are two main factors causing the leakage, one is the main factor affecting the sealing performance, that is, there is a gap between the sealing pair, the other is the pressure difference between the two sides of the sealing pair. The principle of valve sealing is also analyzed from the four aspects of liquid sealing, gas sealing, leakage channel sealing principle and valve sealing pair.

Liquid tightness

The sealing of the liquid is carried out by the viscosity and surface tension of the liquid. When the capillary from which the valve leaks is filled with gas, surface tension may repel the fluid or draw it into the capillary. So that's the tangent Angle. When the tangent Angle is less than 90°, the liquid is injected into the capillary and leakage occurs. Leakage occurs because of the different properties of the medium. Under the same conditions, different results will be obtained when different media are used to do experiments. You can use water, air, kerosene, etc. Leakage also occurs when the tangent Angle is greater than 90°. Because of the grease or waxy film on the metal surface. Once the film on these surfaces is dissolved, the properties of the metal surface change, and the liquid, which was previously repelled, penetrates the surface and leaks. In view of the above situation, according to Poisson's formula, the purpose of preventing leakage or reducing the amount of leakage can be realized on the condition of reducing capillary diameter and medium viscosity.

Gas tightness

According to Poisson's formula, gas tightness is related to gas molecules and gas viscosity. Leakage is inversely proportional to the length of the capillary and the viscosity of the gas, and is directly 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 freedom of the gas molecules, the gas molecules will flow into the capillary with free thermal motion. Therefore, when we do the valve sealing test, the medium must be water to play the role of sealing, with air that gas can not play the role of sealing. Even if we reduce the capillary diameter below the gas molecule by plastic deformation, the flow of gas still cannot be stopped. The reason is that gases can still diffuse through the metal walls. So when we do the gas test, we must be more strict than the liquid test.

Leakage channel sealing principle

The valve seal is composed of two parts: the roughness of the unevenness scattered on the waveform surface and the corrugation of the distance between the peaks. In the case that most of the elastic stress of metal materials in Our country is low, if we want to achieve the sealing state, we need to raise higher requirements on the compression force of metal materials, that is, the compressive force of the material should exceed its elasticity. Therefore, in the design of the valve, the sealing pair combined with a certain hardness difference to match, under the action of pressure, it will produce a certain degree of plastic deformation sealing effect. If the sealing surface is metal material, then the surface of the uneven convex point will be the first to appear, in the initial use of small load can make these uneven convex point plastic deformation. As the contact surface increases, the surface unflatness becomes plastic-elastic deformation. The roughness of both surfaces is present at the concave. These remaining sizes can be closed by applying a load that can cause severe plastic deformation of the underlying material and by keeping the two surfaces in close contact along a continuous line and in a circular direction.

Valve seal pair

The valve seal pair is the part where the seat and the closing part are closed when they contact each other. Metal sealing surface in the process of use, easy to be sandwiched medium, medium corrosion, wear particles, cavitation and erosion damage. Wear particles, for example. If the roughness of the wear particles is smaller than that of the surface, the surface accuracy will be improved rather than deteriorated when the sealing surface runs in. On the contrary, it will deteriorate the surface accuracy. Therefore, in the selection of wear particles, the material, working condition, lubricity and corrosion of sealing surface should be considered comprehensively. As wear particles, when we choose seals, we should consider the various factors affecting their performance, in order to play the function of anti-leakage. Therefore, it is necessary to choose materials that are resistant to corrosion, abrasion and erosion. Otherwise, the lack of any one of the requirements will greatly reduce its sealing performance.