The leakage of dry-running friction seals is never really constant and may even change its magnitude to a significantly different level within a short time, causing a lot of misunder-standings and problems in practice. To investigate the quantities affecting the leakage, different types of packing ring styles made of commonly used dry-running materials were tested undere a wide range of load parameters. The tests showed that, dependign on ring style, material nad load parameters, the flow area of the sealings amy vary considerably-in spite of all wear compensation measures .The flow area variations are caused by rnadom combinations of uneven wear, deformation and rotation of the sealing rings and/or segments, promoted by cold-flow and in some cases brittleness of the widely used PTEE-based dry-running materials. As a consequence there is an unsteady pressure distribution whthin the packing, leading to a non-reproducible and therefore non-prddictable leakage pattern.
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