1. The surface condition of the sealing surface
The shape and surface roughness of the sealing surface have a certain influence on the sealing performance, and the smooth surface is conducive to sealing. Soft gaskets are not sensitive to surface conditions due to their ease of deformation, whereas for hard gaskets, the surface condition has a great influence.
2. The contact width of the sealing surface
The larger the contact width between the sealing surface and the gasket or packing, the longer the path for fluid leakage and the greater the flow resistance loss, which is conducive to sealing. However, under the same pressing force, the larger the contact width, the smaller the sealing specific pressure. Therefore, it is necessary to find an appropriate contact width according to the material of the seal.
3. The nature of the fluid
The viscosity of the liquid has a great influence on the sealing performance of packings and gaskets. Fluids with high viscosity are easy to seal due to their poor fluidity. The viscosity of liquid is much higher than that of gas, so liquid is easier to seal than gas. Saturated steam is easier to seal than superheated steam because it will condense out 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, so it is easier to seal. The wettability of the liquid to the seal material also has a certain influence on the seal. Liquids that are prone to wetting are prone to seepage leakage due to the capillary action of the micropores inside the gasket and packing.
4. Fluid temperature
The level of temperature affects the viscosity of the liquid, thereby affecting the sealing. As the temperature increases, the viscosity of the liquid decreases and the viscosity of the gas increases. On the other hand, the change of temperature often deforms the seal assembly and easily causes leakage.
5. Material of gasket and packing
Soft materials are easy to produce elastic or plastic deformation under the action of pre-tightening force, thereby blocking the passage of fluid leakage, which is conducive to sealing; but soft materials generally cannot withstand the action of high-pressure fluid. The corrosion resistance, heat resistance, compactness, and hydrophilicity of the sealing material all have a certain influence on the sealing.
6. Specific pressure of sealing surface
The normal force on the unit contact surface between the sealing surfaces is called the sealing specific pressure, and the specific pressure of the sealing surface is an important factor affecting the sealing performance of the gasket or packing. Usually, by applying a pre-tightening force to generate a certain specific pressure on the sealing surface, the seal will be deformed to reduce or eliminate the gap between the sealing contact surfaces, prevent the passage of fluid, and achieve the purpose of sealing. It should be pointed out that the effect of fluid pressure will change the specific pressure of the sealing surface. Although the increase in the specific pressure of the sealing surface is beneficial to sealing, it is limited by the extrusion strength of the seal material; for dynamic sealing, the increase in the specific pressure of the sealing surface will also cause a corresponding increase in frictional resistance.
7. Influence of external conditions
The vibration of the pipeline system, the deformation of the connecting components, the deviation of the installation position and other reasons will generate additional force on the seal, which will have an adverse effect on the seal. In particular, vibration will cause periodic changes in the pressing force between the sealing surfaces, causing the connecting bolts to loosen, resulting in seal failure. The cause of the vibration can be external or it can be caused by fluid movement inside the system. To make the seal reliable, the above-mentioned factors must be carefully considered, and the manufacture and selection of sealing gaskets and packings are very important.