The factors that affect the sealing of gaskets and packings are mainly as follows:
1. Surface condition of the sealing surface:
The shape and surface roughness of the sealing surface have a certain influence on the sealing performance, and a smooth surface is conducive to sealing. Soft gaskets are not sensitive to surface conditions because they are easy to deform, while for hard gaskets, the surface conditions have a great influence.
2. Contact width of the sealing surface:
The larger the contact width between the sealing surface and the gasket or packing, the longer the path required for the fluid to leak, and the greater the flow resistance loss, which is conducive to sealing. However, under the same clamping force, the larger the contact width, the smaller the sealing pressure ratio. Therefore, it is necessary to seek a suitable contact width according to the material condition of the seal.
3. Properties of the fluid:
The viscosity of the liquid has a great influence on the sealing performance of the packing and gasket. Fluids with high viscosity are easy to seal because of their poor fluidity. The viscosity of the liquid is much greater than that of the gas, so the liquid is easier to seal than the gas. Saturated steam is easier to seal than superheated steam because it will condense droplets and block the leakage channel between the sealing surfaces. The larger the molecular volume of the fluid, the easier it is to be blocked by the narrow sealing gap, making it easier to seal. The wettability of the liquid to the sealing material also has a certain influence on the sealing. Liquids that are easy to wet are prone to penetration and leakage due to the capillary effect of the micropores inside the gasket and filler.
4. Fluid temperature:
The temperature affects the viscosity of the liquid, which affects the sealing. As the temperature rises, the viscosity of the liquid decreases, and the viscosity of the gas increases. On the other hand, temperature changes often cause the sealing components to deform and easily cause leakage.
5. Gasket and filler material:
Soft materials are easy to deform elastically or plastically under the effect of preload, thereby blocking the channel for fluid leakage, so they are conducive to sealing; but soft materials generally cannot withstand the effect of high-pressure fluids. The corrosion resistance, heat resistance, fineness, hydrophilicity, etc. of the sealing material all have a certain influence on the sealing.
6. Sealing surface pressure ratio:
The normal force on the unit contact surface between the sealing surfaces is called the sealing pressure ratio. The size of the sealing surface pressure ratio is an important factor affecting the sealing performance of the gasket or packing. Generally, a certain pressure ratio is generated on the sealing surface by applying a preload force, so that the seal is deformed to reduce or eliminate the gap between the sealing contact surfaces, prevent the fluid from passing through, and achieve the purpose of sealing. It should be pointed out that the effect of fluid pressure will change the sealing surface pressure ratio. Although the increase in the sealing surface pressure ratio is beneficial to sealing, it is constrained by the extrusion strength of the sealing material; for dynamic sealing, the increase in the sealing surface pressure ratio will also cause a corresponding increase in friction resistance.
7. Influence of external conditions:
The vibration of the pipeline system, the deformation of the connection components, the offset of the installation position, etc. will all generate additional forces on the seal, thereby adversely affecting the seal. In particular, vibration will cause the compression force between the sealing surfaces to change periodically, loosen the connection bolts, and cause the seal to fail. The cause of the vibration may be external or caused by the fluid flow inside the system. To ensure a reliable seal, it is necessary to carefully consider the above factors, and the production and selection of sealing gaskets and packings are crucial.