Seat seals are typically FS (floating seat) or RS (reverse seat) designs. FS seals use a T-seal or dual-lip configuration with PEEK backups; pressure-energized lips ensure sealing at low pressure while the body provides extrusion resistance at 30 ksi in expanding or split-gate valves https://globalsealstech.com/product-category/oil-gas-seals/api-6a-gate-valve-seals/