What was found
"AIR SYS 1 OFF" ANNUNCIATED. AFTER ABOUT A MINUTE GOT "AIR MANF 1 FAIL" LEVEL 3 ALERT. COMPLIED WITH QRH. DIVERTED, DURING DECENT, AIR MANF 1 FAIL ALERT CAME ON SEVERAL TIMES. INTERIGATED MCDU FOUND NO FAULTS IN AIU , VIA, OR PSC1, PERFORMED RTS ON PSC1 AND PASSED. OPENED NR1 ENG AND APPLIED AIR TO SYS FOUND LEAK ON OVERPRESSURE VALVE. REPLACED CLAMPS WITH NO HELP, INSTALLED NEW VALVE AND LEAK CHECKED GOOD. REF AMM 78-31-03-2. PERFORMED DECAY TEST REF 36-00-01-5 TEST PASSED. RAN NR 1 ENG FOR 20 MIN TOTAL AND 5 MINS, AT FLIGHT IDLE, NO FAULTS ON ENGINE RUN. ENG RUN PERFORMED BY EMP 485450. CLOSED NR1 COWLINGS REF AMM 71-00-00-5.