1. Leakage of gaskets

There are four types of leakage phenomenon in general gaskets: interface leakage, penetration leakage, diffusion leakage, and damage leakage.

（1）. Interface leaks

The interface will leak at the sealing interface due to insufficient gasket compression, improper flange joint surface finish, and flange deformation. For interface leakage, it can be prevented by using soft gasket to clamp in the flange face.

（2）. Penetration leakage

Since most of the soft materials are made of fibers, they are easily soaked by the medium, especially the pressure. Due to capillary phenomenon, the medium will permeate to the low pressure side, forming permeation.

（3）.Diffusion leakage

Driven by the concentration difference, the medium leaks through the material transfer generated by the sealing gap or the capillary of the sealing material. Diffusion is the result of molecular motion and is not unidirectional. When the sealing pressure difference is extremely small or in a vacuum state, or when sealing permeable substances such as nitrogen and hydrogen, as well as highly toxic and radioactive substances, special attention should be paid to the leakage and diffusion.

（4）.Destroy the leak

The working conditions of the sealing part are relatively bad, the thermal deformation is large, it is often subjected to vibration, impact, improper installation, excessive tightening force, repeated use, compression deformation, internal stress concentration, damage beyond the fatigue strength, material aging, deterioration, etc. will cause damage to leaks. This kind of leakage has the greatest impact and great harm, so it is necessary to strengthen prevention.

2. Gasket sealing mechanism

The function of the gasket is caused by the blocking effect on the internal medium formed by the contact pressure of the sealing material on the joint surface and the elastic restoring force to the external tightening force.

3. Classification and structure of gaskets

Gaskets are divided into three categories: non-metallic gaskets, non-metallic and metal combined gaskets and metal gaskets. The common materials are rubber, leather, asbestos board, cork, PTFE, tinplate, steel, aluminum, copper and stainless steel.

4. the selection of gaskets

The selection principle of the gasket: according to the working pressure, working temperature, the corrosiveness of the sealing medium and the form of the sealing surface.

（1）. Temperature influence

In normal temperature and low pressure, use non-metallic soft honey gasket; in medium pressure and high temperature, choose metal and non-metal combination gasket or metal gasket; when temperature and pressure fluctuate greatly, choose good elasticity or self-tightening type Gaskets; in low temperature, corrosive media or vacuum conditions, gaskets with special properties should be considered.

（2）.Influence of flange form

Different flange forms require different gaskets. Smooth-faced flanges are generally only used for low pressure, with soft thin gaskets; under high pressure, if the strength of the flange is sufficient, smooth-faced flanges can also be used, but thick soft gaskets should be used, or inner belt reinforcement should be used. Wound gasket for ring or reinforcement ring. In this case, metal gaskets are also not suitable, because the required pressing force is too large, resulting in large deformation of the bolts, making the flange difficult to seal. If a metal gasket is to be used, the smooth surface should be reduced to reduce the contact area with the gasket. In this way, under the condition of the same bolt tension, the compressive stress of the reduced narrow smooth surface will increase.