What was found
AFTER T/O AT APPROX 6000 MSG BLEED OVERPPRESSURE 1 AND 2 BECAME ANNUNCIATED WITH CAUTION ADVISORY. PACK 1 AND 2 FAIL ANNUNCIATED FOLLOWED A/C RETURNING TO DEPARTURE LESS FPM 100 PER MINUTE ON LANDING. REMOVED AND REPLACED LT AND RT ENGINE PRESSURE REGULATING SHUTOFF VALVES IAW AMM 36-11-03-000-801-A AND 36-11-03-400-801-A. NO LEAKS NOTED. OP CHECKED GOOD. REMOVED AND REPLACED RT NPRSV IAW AMM 36-11-03. PERFORMED RH ENGINE LEAK CHECK IAW EMB 175 AMM 36-11-03-790-801. NO LEAKS NOTED. OP CHECKED GOOD. INSTALLED ENGINE #1 NACELLE PRESSURE REGULATING SHUTOFF VAVLE IAW EMB 175 AMM 36-11-03-400-801-A. OP CHECKED GOOD. NO LEAKS NOTED.