What are the basic conditions for sealing? What is the sealing specific pressure? What is the gasket coefficient? Why school

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This post was last edited by *aoye613 on 2010-1-5 at 18:38. There are two conditions for forced sealing with gaskets: the pre-sealing condition and the operational sealing condition. The significance of pre-sealing conditions is that, no matter how precisely the sealing surfaces of the flanges are machined, on a microscopic level their surfaces are always uneven and contain grooves. These grooves can become leakage paths for the sealing surface. Therefore, softer gaskets must be used; under the force of the pre-tightening bolts, the surface of these gaskets will press into the uneven areas of the flange sealing surface, filling in the grooves and eliminating the aforementioned leakage paths. To this end, there must be sufficient compressive force on the effective sealing area per gasket unit. The compressive force per unit area is called the gasket sealing specific pressure (in MPa), denoted by y. Different gaskets have different specific pressures. The harder the gasket material, the higher y is. The purpose of operating under sealing conditions is as follows: For a sealing surface that has achieved a pre-sealing condition through pre-tightening, under the action of internal pressure, the axial force exerted by the pressure causes the sealing surfaces to separate, which reduces the compressive force between the gasket and the sealing surfaces and creates tiny gaps. As a result, the medium under internal pressure may leak through these gaps. To ensure its sealing, a sufficient fluid resistance must be maintained between the gasket and the sealing surface; only when this resistance is greater than the driving force caused by the pressure difference between the inside and outside of the medium can the gasket provide a seal and prevent leakage. Since the fluid resistance between the gasket and the sealing surface is proportional to the gasket compression force, it is necessary to maintain a sufficiently high compression force between them in order to ensure that the gap remains small enough so as to result in a high enough fluid resistance. The ratio of the compressive force applied per unit effective sealing area of the gasket to its internal pressure, when this force maintains a sufficient resistance between the gasket and the flange sealing surface to prevent leakage, is called the gasket coefficient, denoted by m. Different gaskets have different m values, and m increases as the hardness of the gasket increases. The gasket experiences the greatest compressive force when the bolts are tightened, and it may be compressed to the point of plastic deformation, losing its ability to rebound. When the flange sealing surfaces separate due to the pressure of the medium, the gasket is unable to rebound and re-press against those sealing surfaces, resulting in insufficient contact force (i.e., gasket compression force) and thus leakage. Therefore, when the gasket is pre-tightened, it must be compressed enough so that the compressive force per unit effective sealing area is not less than the value of y, yet the compressive force must not be too high to prevent plastic deformation. In the case of planar sealing, to prevent the gasket from being plastically deformed, the pre-tightening force on the gasket should be kept at no more than 4y. When the gasket is pre-tightened, if the compressive force per unit of effective sealing area is less than y, it will prevent the elimination of \"leakage paths,\" thus failing to meet the requirements for pre-sealing ； Conversely, when the gasket preload is too high (>4y), the gasket loses its elasticity, which causes leakage under internal pressure. The verification of the minimum width of the gasket in gasket calculations serves this purpose. However, this verification allows for substitution with experience; that is, the minimum width of the gasket can be determined empirically (as per the relevant gasket standards). When inexperienced, it is recommended to conduct verification to ensure the reliability of the seal.