Right.ValveThe sealing function is required to prevent leakage. According to the different parts and degree of the leakage, the leakage of the valve is different, so it is necessary to put forward different methods.

There are two reasons for leakage, one is the most important factor affecting the sealing performance, that is, there is a gap between the sealing pair, and the other is the pressure difference between the two sides of the sealing pair. The principle of valve sealing is also analyzed from four aspects: liquid sealing, gas sealing, leakage channel sealing principle and valve sealing vice.

1, the tightness of the liquid

The sealing of the liquid is carried out by the viscosity and surface tension of the liquid. When a leaking capillary is filled with gas, surface tension forces repel or introduce liquid into the capillary. This creates a phase cut angle. When the phase cut angle is less than 90 °, the liquid will be injected into the capillary and leakage will occur. The reason for the leakage lies in the different nature of the medium. With different media to do the test, in the case of equal conditions, will get different results. Can use water, air, kerosene, etc. Leakage also occurs when the phase cut angle is greater than 90 °. Because it is related to the grease or wax film on the metal surface. When the film on these surfaces is dissolved, the characteristics of the metal surface have undergone some changes, and the originally repelled liquid will invade the surface and cause leakage.

2. Gas tightness

The tightness of the 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 and the average degree of freedom of the gas molecules are the same, the gas molecules will flow into the capillary with free thermal motion. Therefore, when we are doing the valve seal test, the medium must be water to play the role of sealing, with air that is, gas can not play the role of sealing. Even if we reduce the capillary diameter below the gas molecule by plastic deformation, we still cannot stop the flow of gas. The reason is that the gas can still diffuse through the metal wall.Wuhan Xiete Valve Technology Co., Ltd.In the gas test, more rigorous than the liquid test.

3. Sealing principle of leakage channel

The valve seal consists of two parts: the roughness of the unevenness spread on the wave surface and the waviness of the distance between the waves. In most of the metal materials in our country elastic strain force is low, if you want to achieve the state of sealing, you need to put a higher demand on the compression force of metal materials, that is, the compression force of the material should exceed its elasticity. Therefore, in the valve design, the sealing pair is matched with a certain hardness difference, and under the action of pressure, it will produce a certain degree of plastic deformation and sealing effect. If the sealing surface is a metal material, then the surface of the uneven protruding point will be the earliest, in the initial only with a small load can make these uneven protruding point plastic deformation. When the contact surface increases, the unevenness of the surface will become plastic-elastic deformation. At this time, the roughness of both sides in the recess will exist. When it is necessary to apply a load that can cause severe plastic deformation of the underlying material, and make the two surfaces contact closely, these remaining diameters can be closed along the continuous line and the ring direction.

4. Valve seal pair

Valve sealing pair is the part of the valve seat and the closing member that closes when they are in contact with each other. Metal sealing surface in the use of the process, vulnerable to the inclusion of media, media corrosion, wear particles, cavitation and erosion of the damage. Like wear particles. If the wear particles are smaller than the surface roughness, the surface accuracy of the sealing surface will be improved without deterioration. On the contrary, the surface accuracy will be deteriorated. Therefore, when selecting wear particles, it is necessary to comprehensively consider its material, working conditions, lubricity and corrosion of the sealing surface. Like wear particles, when we choose a seal, we must comprehensively consider various factors that affect its performance in order to prevent leakage. Therefore, it is necessary to choose those materials that are resistant to corrosion, abrasion and erosion. Otherwise, the lack of any requirement will greatly reduce its sealing performance.