It is also subject to issues with decompression after it has been highly pressurized and should not be exposed to temperature fluctuations greater than 167☏. Note, however, that the temperature performance of virgin PTFE is highly dependent on the operating pressure.Īmong the drawbacks of PTFE is its susceptibility to cold creep, is best for temperatures no greater than 5 ksi, and has limited performance in the presence of radiation due to a maximum lifetime radiation dose of 1×10 4 rads. Its operating temperature range includes cryogenic temperatures between -429☏ and 400☏. In addition, its chemical compatibility works well with a wide range of media with the exception of fluorine and liquid alkalis. The chemical compatibility and high-temperature performance of PTFE mean it works well with applications that involve sanitation and sterilization. It is also fire resistant, hydrophobic, and non-wetting It has both a low coefficient of thermal expansion and a good coefficient of hygroscopic expansions, making it stable dimensionally. It possesses enough ductility to provide a good seal, even in the presence of extreme temperatures and highly corrosive materials. PTFE provides excellent wear resistance and good stress recovery, which can be enhanced by the right choice of additives. This polymer is also capable of dry running (and thus requires no lubricants) and exhibits no stick-slip behavior. Virgin PTFE has the lowest coefficient of friction of any thermoplastic in existence (even geckos cannot maintain their grip on Teflon) and filled-PTFE grades are available with very low friction as well. PTFE (trade name Teflon) has long been a popular choice for ball valve seat materials and is available in FDA-approved grades. In addition, there may be a need for materials to be flame retardant, fire-resistant, or suitable for use in environments with radiation. And if there is extended exposure to water or humidity, a ball valve seat must have a low coefficient of hygroscopic expansion. These can include dimensional stability and reliable performance at extreme temperatures (which may include cryogenic) as well as the ability to withstand sterilization routines that involve hot water, steam, and/or caustic cleaning materials. There are other considerations involved as well, with many depending on the operating environment. Material Properties for Harsh Environments And while there are a variety of polymer materials that can be used, PTFE, filled-PTFE, and PEEK are the most commonly used. If the ball valves are used in connection with food, dairy, or pharmaceutical applications, they may also require materials that are FDA approved.
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