Views:93 Author:Site Editor Publish Time: 2020-09-18 Origin:Site
1 Compressed Thickness of Gaskets
How to choose the proper thickness of gaskets is a practical problem. The gasket thickness is related to the leakage rate. In industry, the thicker gasket is needed and highly recommended. It is known to us that the industrial equipment, like stainless stel tank or Pressurized vessel, is very thick. The reasons are as follows:
(1) Under the same medium and the same pressure. the rate of leakage will decline as the thickness of the gasket increases. The reason is under the same axial load force, compared to the thin gaskets, the resilience of the thick gasket is better. It will compensate for the separation of the flange surface which is caused by pressure and temperature so that it will improve the sealing performance.Thus, there is no wonder the thickness of the crude oil distillation column is large.
(2) A large number of bolting is not needed in large diameter flanges if the gasket thickness is thick and the pressure is relatively low. The design does not require a good deal of bolting since the internal pressure is relatively low. Limited bolting means there will be low compression of the gasket, and thin flanges will distort when bolted, which means the compression in the space between bolts is not enough. Thus, there is a high risk of leakage of the medium.
However, it should be pointed out that the thickness of the gasket should be in a certain range, it does not mean increasing thickness would enhance the sealing performance. The reason is under different thicknesses the initial working conditions are different. The stress of the gasket surface is influenced by friction, so the material is easier to deform. Nevertheless, the middle part of the gasket is likely to have plastic deformation because the friction does not have a great effect on it. Therefore, the sealing property is not improved even though the thickness is increasing. What is more, the thick gasket means the area of leakage surface is large, which causes leakage rate to increase.
The selection of gasket material depends on the working environment and its applications. All gasket material will lose their resilience as time goes by because of applied pressure, temperature and aging. Under different situations, the raw materials for gasket/seals/seat are different.The food grade butterfly valve is normally using rubber gaskets.such as EPDM,Silicone,Viton,NBR. while the hygienic ball valve is likely to use PTFE gaskets.