Anti-extrusion systems for seat and stem seals use PEEK, woven aramid/PTFE, or metal spring expanders. They prevent elastomer flow at 25,000 psi differential and 250°C continuous, standard in deepwater and ultra-HPHT gate valves requiring 30-year life. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-gate-valve-seals/