1. Surface Condition of the Sealing Surface: The shape and surface roughness of the sealing surface have a certain impact on the sealing performance. A smooth surface is beneficial for sealing. Soft gaskets are not sensitive to surface conditions because they are easily deformed, while the surface condition has a significant impact on hard gaskets.
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 fluid leakage, and the greater the flow resistance loss, thus benefiting the seal. However, under the same clamping force, a larger contact width will reduce the sealing specific pressure. Therefore, an appropriate contact width should be sought based on the material of the sealing component.
3. Properties of the Sealing Fluid: The viscosity of the liquid has a significant impact on the sealing performance of packing and gaskets. Fluids with high viscosity are easier to seal due to their poor flowability. The viscosity of liquids is much greater than that of gases, so liquids are easier to seal than gases. Saturated vapor is easier to seal than superheated vapor because it condenses into droplets that block the leakage channel between the sealing surfaces. The larger the molecular volume of a fluid, the easier it is to be blocked by narrow sealing gaps, thus facilitating sealing. The wettability of the liquid to the sealing material also affects the seal. Easily wetted liquids are prone to leakage due to capillary action within the micropores of the gasket and packing.
4. Temperature of the sealing fluid: Temperature affects the viscosity of the liquid, thus influencing the sealing performance. Increased temperature decreases liquid viscosity and increases gas viscosity. Furthermore, temperature changes often cause deformation of the sealing components, making them more prone to leakage.
5. Material of the sealing gasket and packing: Soft materials are more likely to undergo elastic or plastic deformation under preload, thus blocking leakage channels and promoting sealing; however, soft materials generally cannot withstand high-pressure fluids. The corrosion resistance, heat resistance, density, and hydrophilicity of the sealing material all have a certain impact on the seal.
6. Sealing surface specific pressure: The normal force per unit contact surface between sealing surfaces is called the sealing specific pressure. The magnitude of the sealing surface specific pressure is an important factor affecting the sealing performance of gaskets or packings. Typically, a certain specific pressure is generated on the sealing surface by applying a preload, causing the seal to deform and reduce or eliminate gaps between the sealing contact surfaces, thus preventing fluid passage and achieving a seal. It should be noted that fluid pressure causes changes in the specific pressure of the sealing surface. While an increase in the specific pressure of the sealing surface is beneficial for sealing, it is limited by the compressive strength of the sealing material; for dynamic seals, an increase in the specific pressure of the sealing surface will also lead to a corresponding increase in frictional resistance.
7. External Factors Affecting the Seal: Vibration of the piping system, deformation of connecting components, and misalignment of the installation position can all exert additional forces on the seal, thus adversely affecting the seal. Vibration, in particular, will cause periodic changes in the clamping force between the sealing surfaces, loosening the connecting bolts and causing seal failure. The causes of vibration may be external or due to fluid movement within the system. To ensure a reliable seal, all of the above factors must be carefully considered, and the manufacture and selection of gaskets and packings are crucial.
