Factors affecting gasket and packing seal
- (1) Surface condition of sealing surface: the shape and surface roughness of sealing surface have certain influence on sealing performance, and smooth surface is beneficial to sealing. The soft gasket is insensitive to the surface condition because of its easy deformation, while the hard gasket is greatly affected by the surface condition.
- (2) Contact width of sealing surface: the larger the contact width between sealing surface and gasket or filler, the longer the path of fluid leakage, the greater the loss of flow resistance, thus conducive to sealing. But under the same compression force, the larger the contact width, the lower the sealing pressure. Therefore, the appropriate contact width should be sought according to the material quality of the seals.
- (3) Properties of the fluid: The viscosity of the liquid has a great influence on the sealing of the packing and gasket. The fluid with high viscosity is easy to seal because of its poor fluidity. The viscosity of the liquid is much larger than that of the gas, so the liquid is easier to seal than the gas. Saturated vapor is easier to seal than superheated vapor because it will condensate droplets and block the passage between the sealing surfaces. The larger the molecular volume of the fluid is, the easier it is to be blocked by a narrow sealing gap, which is easy to seal. The wettability of liquid to seal material also has a certain effect on sealing. The liquid which is easy to soak is easy to produce leakage due to the capillary action of the micro-pores in the gasket and filler.
- (4) the temperature of the fluid: the temperature affects the viscosity of the liquid, thereby affecting the sealing performance. When the temperature increases, the viscosity of the liquid decreases and the viscosity of the gas increases. On the other hand, temperature changes often deform the seal assembly and cause leakage easily.
- Material of gaskets and fillers: Soft materials are prone to elastic or plastic deformation under preloading force, thus blocking the passage of fluid leakage, 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 sealing materials have certain effects on sealing.
Specific pressure of sealing surface:
The normal force acting on the unit contact surface between sealing surface is called the sealing specific pressure. The sealing surface specific pressure is an important factor affecting the sealing performance of gaskets or packing. Usually, by applying pre-tightening force on the sealing surface to produce a certain specific pressure, so that the deformation of the seal to reduce or eliminate the gap between the sealing contact surfaces, to prevent the flow through, to achieve the purpose of sealing. It should be pointed out that the effect of fluid pressure will change the relative pressure of the sealing surface. Although the increase of specific pressure of sealing surface is beneficial to sealing, it is limited by the extrusion strength of sealing material. For dynamic sealing, the increase of specific pressure of sealing surface will also cause the corresponding increase of friction resistance.
Influence of external conditions: vibration of pipeline system, deformation of connecting components, offset of installation position and other reasons will produce additional force on the seal, thus causing adverse effects on the seal. Especially, vibration will cause periodic changes in the pressure between the sealing surfaces, so that the connection bolt relaxation, resulting in seal failure. The cause of vibration may be external or possibly caused by fluid flow inside the system. In order to make the seal reliable, the above factors must be carefully considered, and the manufacture and selection of gaskets and fillers are very important.
Source: China Stainless Steel Gaskets Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)