What was found
AT FLIGHT LEVEL 410 NR 1 BLEED TRIP. RAN QRH AND THE TRIP RESET SUCCESSFULLY. 30 SECONDS LATER, THE NR 1 BLEED TRIP OFF LIGHT REILLUMINATED. WE CONTINUED TO RUN THE QRH WITH THE BLEED TRIP OFF LIGHT NOT RESTTING. 30 SECONDS LATER, THE NR 2 BLEED TRIPPED. WE DID AN EMERGENCY DECENT. O2 MASKS DEPLOYED. PERFORMED A BLEED AIR SYS HEALTH OF NR 1 ENGINE IAW AMM 36-11-00-700-801. THE HIGH STAGE REG FAILED THE REVERSE FLOW DIAPHRAM. R & R NR 1 HIGH STAGE REG IAW AMM 36-11-07, R & R THE NR 1 ENGINE 450 AND 390 THERMOSTAT SENSOR IAW 36-11-05. PERFORMED A BLEED AIR SYS HEALTH CHECK OF NR 2 ENGINE IAW AMM 36-11-00-700-801. THE PRECOOLER CONTROL VALVE, PC PRESSURE WAS OUT OF RANGE. R & R THE NR 2 ENGINE PRECOOLER CONTROL VALVE IAW AMM 36-12-02. R & R OXYGEN GENERATORS.