Air Products recommends specific washer materials for certain applications. Nylon gaskets are recommended for medical yoke connections, while fiber washers are commonly used in carbon dioxide service. PTFE is compatible with most gases and is the most common washer material used with specialty gases. However, PTFE has some properties that can make it a poor choice for a washer material. It has a tendency to cold-flow. Cold flow occurs when pressure is applied to the material, and it flows away from the pressure. This can cause leaks to develop as the washer moves, reducing the sealing pressure on the washer. The flowing washer material can also restrict flow paths and jam in the connection threads. PTFE is also permeable to moisture and oxygen, which can cause micro contamination in sensitive processes.

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