What was found
RT ENG BLEED OFF LIGHT CAME ON AT FL 340, CABIN CLIMBED RAPIDLY EMERGENCY DESCENT RETURN TO DEPARTURE. LT ENG BLEED VALVE WAS DEFERRED IAW. T/S SYS IAW FIM 36-10-00, FOUND "B" NOT LEAKING AT 490 DEGREE SWITCH, REMOVE LINE CLEAN REINSTALLED, NO LEAKS NOTED, BLEED PS CHECK NORMAL IAW 36-11-00, REMOVED AND REPLACED, LT CONTROL REVERSE FLOW CHECK IAW MM 36-11-18, REMOVED AND REPLACED LT PRSOV IAW MM 36-11-09, ALSO REMOVED AND REPLACED LT PILOT HIGH STAGE.