①Surface 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 good for sealing. Soft gaskets are not sensitive to surface conditions due to their easy deformation, while for hard gaskets, the surface conditions have a great influence.
②The contact width of the sealing surface: The larger the contact width between the sealing surface and the gasket or packing, the longer the path through which the fluid leaks, and the greater the flow resistance loss, which is beneficial to sealing. But under the same pressing force, the greater the contact width, the smaller the seal specific pressure. Therefore, it is necessary to find an appropriate contact width according to the material of the seal.
③The properties of the sealing fluid: The viscosity of the liquid has a great influence on the sealing performance of the packing and gasket. The fluid with high viscosity is easy to seal due to its poor fluidity. The viscosity of liquid is much greater 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 droplets and block the leaking passage between the sealing surfaces. The larger the molecular volume of the fluid, the easier it is to be blocked by the narrow sealing gap, thus making it easier to seal. The wettability of the liquid to the seal material also has a certain effect on the seal. Liquids that are easy to infiltrate are prone to permeate leakage due to the capillary action of the micropores inside the gasket and the filler.
④Temperature of the sealing fluid: The temperature affects the viscosity of the liquid, thereby affecting the sealing performance. As the temperature increases, the viscosity of the liquid decreases, and the viscosity of the gas increases. On the other hand, changes in temperature often deform the sealing assembly and easily cause leakage.
⑤Material of sealing gasket and packing: soft materials are easy to produce elastic or plastic deformation under the action of pre-tensioning force, thereby blocking fluid leakage channels, 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.
⑥Sealing surface specific pressure: The normal force on the unit contact surface between the sealing surfaces is called the sealing specific pressure. The specific pressure of the sealing surface is an important factor that affects the sealing performance of the gasket or packing. Generally, a certain specific pressure is generated on the sealing surface by applying a pre-tightening force to deform the sealing element 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 conducive to sealing, it is limited by the extrusion strength of the seal material; for dynamic seals, the increase in the specific pressure of the sealing surface will also cause a corresponding increase in friction resistance.
⑦The influence of external conditions of the seal: the vibration of the piping system, the deformation of the connecting components, the deviation of the installation position and other reasons will produce additional force on the seal, which will adversely affect the seal. In particular, vibration will cause periodic changes in the pressing force between the sealing surfaces, which will loosen the connecting bolts and cause seal failure. The cause of vibration may be external, or it may 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 gaskets and fillers are very important.