The sealing gasket serves the critical function of preventing leakage, specifically ensuring that liquids, gases, or even fine particles do not escape through the gasket’s sealing connection. For pumps, the substances being sealed typically include liquids, gases, or even dust. When it comes to gasket sealing failures, two primary scenarios often lead to leakage: first, there are gaps present on the sealing surface; second, there is a pressure differential across the sealing area. Addressing these issues involves minimizing or eliminating the gaps between the sealing surfaces. These gaps may exist between the surfaces themselves or within the sealing device.
One of the leading causes of gasket failure-related leaks stems from the compression stress applied to the gasket. To ensure proper sealing, adequate pressure must be applied to the gasket to induce either elastic or plastic deformation, effectively filling the irregularities of the sealing surface. However, if the compression force isn’t properly maintained during assembly or if vibrations loosen the bolts over time, the gasket can fail. Additionally, material aging and deformation can compromise the gasket's integrity. Applying excessive compressive stress can also damage the gasket, destroying its ability to rebound and compensate for any separation between flange surfaces due to temperature or pressure changes. This leads to a dramatic increase in leakage rates. Thus, maintaining the compression stress within a specific range is crucial for preserving an effective seal.
Another significant issue arises from inconsistencies in the internal structure or thickness of the gasket material. A gasket made of flawed materials, such as cardboard with cracks or wrinkles, inherently creates voids within itself. When force is applied, if the gasket’s elastic deformation fails to fully close these gaps, leakage becomes unavoidable.
Working conditions also play a pivotal role in gasket sealing effectiveness. Different pressures and temperatures affect leakage rates, with pressure differences across the sealing surface being the primary driving force for leaks. Higher pressure differences make it easier for the medium to overcome resistance and leak. Temperature significantly impacts sealing performance. Research shows that both elastic and plastic deformation of gaskets increase with rising temperatures, but their rebound performance decreases. Creep variables also rise with temperature. Moreover, as temperature increases, the gasket undergoes accelerated aging, weight loss, creep, and relaxation. Temperature also affects the viscosity of the medium—lower viscosity in liquids and higher viscosity in gases at elevated temperatures increase the likelihood of leakage.
Material compatibility is another concern. Given the diverse chemical properties of pumped substances and the additives used to enhance fuel combustion or alter combustion products, choosing a gasket material that matches the conveyed medium is challenging, often leading to leaks due to incompatibility.
Gasket dimensions also influence sealing performance. Thicker gaskets reduce leakage rates under the same compression load and medium pressure since they offer greater elastic reserves to compensate for surface separations. However, beyond a certain thickness, sealing performance may plateau or decline. Thicker gaskets also increase the area available for permeation leaks, raising the risk.
Similarly, gasket width impacts leakage rates. Within a certain range, increasing the width reduces leakage linearly due to longer leakage channels. Yet, wider gaskets require more bolt force, which may not always be practical.
Leakage essentially represents the flow of medium through space, moving from one confined area to another. The driving force behind this flow stems from pressure or concentration differences. Leaks typically occur at interfaces where there is both a potential leakage path and a pressure differential.
Manufacturing processes inevitably introduce inaccuracies, creating gaps on sealing surfaces that hinder perfect alignment. Hard surfaces lacking plastic deformation, like flanged joints, are particularly prone to leaks, especially with gases and liquids.
To mitigate leaks, two approaches are essential: reducing the leakage cross-section and diminishing the driving forces for leakage. Using a sealing gasket is ideal because preloading fills surface irregularities, blocking leakage paths. Gaskets enable plastic deformation under compression, smoothing out minor imperfections and achieving a seal.
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