What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO SFO DUE TO THE FLIGHT CREW REPORTING THAT A VENT SKIN VALVE FAULT CAME ON AFTER TAKEOFF. THE FLIGHT CREW APPLIED ECAM PROCEDURES AND WAS UNABLE TO MAINTAIN CABIN PRESSURE ALTITUDE VIA MANUAL MODE. THE AIRCRAFT LANDED SAFELY AT SFO AND TAXIED TO THE GATE UNDER ITS OWN POWER. MAINTENANCE FOUND THE SKIN AIR OUTLET VALVE VENT DUCT RUPTURED AND REPLACED IT PER AMM 21-26-00. A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED WITH NO FAULTS NOTED.