What material is used in spray gun valves to prevent air leaks?

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The key idea is dynamic sealing around a moving valve stem. In spray gun valves, air must flow to control atomization, and the stem moves as the valve opens and closes. To prevent air from leaking around that moving stem, a packing material is compressed inside the packing gland to create a tight, enduring seal as the stem slides. This air valve packing is designed to resist solvents and hold up under pressure, providing a reliable seal through many cycles.

O-rings and gaskets are great for static seals where parts don’t move relative to each other, but they aren’t the ideal choice for sealing around a moving valve stem inside a spray gun. Sealants aren’t used as a long-term seal inside the valve for this purpose, since they don’t offer the durable, reusable seal needed for a working valve handle repeated operation. Air valve packing is the appropriate choice because it specifically provides the necessary dynamic seal around the moving stem to prevent air leaks.