Liner hangers use Downhole Seal Stacks for cement retention, with EPDM O-rings in chevrons sealing post-set. Energized by slips, they hold 5,000 PSI differentials. FFKM upgrades for sour service resist surfactants. Lab tests per ISO 14310 show no leaks after 72-hour holds. Gulf completions report 98% success rates. https://globalsealstech.com/media/