What was found
AFTER A NO ENGINE BLEED TAKEOFF, THE RT BLEED TRIPPED OFF DURING THE RECONFIGURING OF THE BLEED AIR SYS. BEFORE THE NON-NORMAL CHECKLIST COULD BE COMPLETED, LT BLEED TRIPPED OFF AS WELL. NON NORMAL CHECKLIST WAS CARRIED OUT AND A TRIP RESET RESTORED BOTH RT AND LT BLEED AIR SYS. ACFT RETURNED FOR A BLEED AIR SYS HEALTH CHECK AND AN ENGINE BLEED AIR CROSSOVER OPS CHECK. THE NR 1 ENG WAS FOUND TO HAVE A FAULT WITH THE PRE COOLER CONTROL VALVE AND ENG 2 HAD A FAULT ON PRESSURE REGULATING SHUTOFF VALVE AND BOTH VALVES WERE REPLACED. AS ADDED INFORMATION THE PREVIOUS FLIGHT HAD A PILOT REPORT OF A DUCT PRESSURE SPLIT IN CLIMB (RT 45, LT 16) THAT WAS RECTIFED WITH REPLACMENT OF THE LT 390 AND LT 450 SENSORS.