High-pressure sealing

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High-pressure sealing: There are many types of high-pressure sealing, which can be divided into forced sealing and self-sealing categories based on their working principles. Forced sealing relies on the pre-tightening force of the connecting elements (bolts) to ensure a certain contact pressure between the top cover of the pressure vessel, the sealing element, and the end of the cylinder body, thereby achieving sealing. Self-sealing is achieved as the operating pressure inside the pressure vessel increases, which in turn raises the contact pressure between the sealing element and the top cover as well as the ends of the cylinder body. The characteristic of self-sealing is that the higher the pressure, the greater the compressive force on the contact surface between the sealing elements, resulting in better sealing performance; moreover, the seal remains reliable even when operating conditions fluctuate. However, its structure is relatively complex, making it difficult to manufacture. Self-sealing can also be divided into axial self-sealing and radial self-sealing based on the deformation mode of the sealing element. Based on the properties of the sealing material, high-pressure sealing can be further divided into plastic sealing, which causes plastic deformation of the sealing element, and elastic sealing, which causes elastic deformation of the sealing element. Currently, the common sealing types used for pressure vessels are as follows: 1. Forced sealing includes flat gasket sealing, cartridge sealing, and octagonal gasket sealing ； 2. Semi-self-sealing type features a double-cone seal ； 3. Self-sealing types include wedge seals, PTFE seals, hollow metal O-ring seals, C-ring seals, B-ring seals, triangular gasket seals, octagonal gasket seals, flat gasket self-sealing systems, and rubber O-ring seals, among others. X. Vacuum Sealing: The sealing performance of a vacuum online system depends on leaks at the connections as well as the outgassing of the vacuum materials. For any vacuum system, it is generally expected that the amount of leakage and gas release is related to various factors such as the type of sealing, the sealing materials, manufacturing precision, and assembly quality. Therefore, there is always a certain level of leakage and gas release at the connections. Accordingly, requirements can be set based on the nature of the vacuum system’s operation, the level of stress experienced by the vacuum chamber, and the speed of gas extraction at its outlet. Synthetic rubber, epoxy resin, and plastics are widely used in vacuum systems where the pressure is in the range above 10-5 Pa. When the vacuum level reaches the range of 10-7 Pa, these sealing materials can no longer be used; ultra-high vacuum sealing materials such as gold or copper must be employed as gaskets, and the vacuum chamber cannot be made of soft materials – it must instead be constructed from stainless steel. The gas state in an ultra-high vacuum is in a state of dynamic equilibrium. The pressure limit within the system is related, on the one hand, to the effective pumping speed of the pump, and on the other hand, to the gas flow rate coming from the vacuum chamber and its internal components. Although there is an effective pumping speed provided by the system, practical limitations always exist due to the structural dimensions and cost of the pump. Therefore, reducing the gas flow rate becomes the basic design goal for achieving an ultra-high vacuum state, and it serves as the main criterion for selecting ultra-high vacuum materials. As materials for use inside vacuum systems, a low saturated vapor pressure is required. To reduce chronic desorption and outgassing, they must be able to withstand baking at high temperatures of 450°C without a loss in mechanical strength or suffering any chemical or physical damage. As a material for vacuum system housings, it is required to have negligible gas permeability, be able to withstand atmospheric pressure, resist air erosion during baking, and not experience leaks. Furthermore, it is required that the materials chosen be easy to process and manufacture, and be inexpensive and readily available. For ultra-high vacuum conditions with a vacuum level below 10-7 Pa, natural and synthetic rubbers are ideal materials for seals: they have good elasticity, the flange bolts experience little stress after being used to create a vacuum seal, and they can be reused multiple times. However, since ultra-high vacuum systems require seal ring materials to withstand baking at 250°C, none of the several rubber materials available actually meet this requirement. For ultra-high vacuum, which has a higher degree of vacuum (i.e., lower pressure), metal seals must be used.