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Seven factors that affect gaskets and packing seals
- Jun 15, 2018 -

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 the surface is smooth to facilitate sealing. Soft gaskets are insensitive to surface conditions because they are prone to deformation, whereas surface conditions are highly influential for hard gaskets.

2 Contact width of the sealing surface: The greater the contact width between the sealing surface and the gasket or packing, the longer the path that the fluid leaks through and the greater the flow resistance loss, which is advantageous for sealing. However, with the same pressing force, the greater the contact width, the lower the sealing specific pressure. Therefore, according to the material of the seal to find the appropriate contact width.

3 Fluid properties: The viscosity of the liquid has a great influence on the sealability of the packing and the gasket. The fluid with a large viscosity is easy to seal due to its poor fluidity. The viscosity of liquid is much larger than that of gas, so the liquid is easier to seal than gas. Saturated steam is easier to seal than superheated steam because it condenses out droplets and blocks the 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 and thus easier to seal. The liquid's wettability with the seal material also has a certain influence on the seal. Liquids that are prone to infiltration are prone to osmotic leakage due to the capillary action of the gasket and the pores inside the packing.

4 fluid temperature: the temperature of the liquid viscosity, thus affecting the seal. As the temperature rises, the viscosity of the liquid decreases, and the viscosity of the gas increases. On the other hand, changes in temperature often cause the seal assembly to deform and tend to cause leakage.

5 gasket and filler material: soft material due to its pre-tightening force is easy to produce elastic or plastic deformation, thereby blocking the passage of fluid leakage, and thus conducive to sealing; but soft materials generally can not withstand the role of high-pressure fluid. The corrosion resistance, heat resistance, compactness, and hydrophilicity of the sealing material 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 sealing specific pressure, and the ratio of the sealing surface pressure is an important factor affecting the gasket or packing sealability. Generally, a certain specific pressure is generated on the sealing surface by applying a pre-tightening force, so that the sealing member is deformed to reduce or eliminate the gap between the sealing contact surfaces and prevent the fluid from passing through to achieve the purpose of sealing. It should be noted that the effect of fluid pressure will cause the sealing surface to change in pressure. Although the increase of the specific pressure of the sealing surface is beneficial to the sealing, it is limited by the compression strength of the sealing material; for the dynamic sealing, the increase of the specific pressure of the sealing surface will also cause a corresponding increase in the frictional resistance.

7 Influence of external conditions: The vibration of the piping system, the deformation of the connection assembly, the offset of the installation position and other reasons will exert additional force on the seal, thus adversely affecting the seal. Vibration, in particular, will cause cyclical changes in the pressing force between the sealing surfaces, loosening the connecting bolts and causing seal failure. The cause of the vibration may be external or it may be caused by fluid inside the system. To make the seal reliable, the above factors must be carefully considered, and the manufacture and selection of sealing gaskets and fillers are of utmost importance.