MECHANIC REPORTS ABOUT AN AIR TURNBACK OF A B757-200; AFTER HE REPLACED THE FORWARD OUTFLOW VALVE. NEW VALVE INSTALLED; WAS FOUND NOT EFFECTIVE FOR THE AIRCRAFT; BUT THE SAME VALVE PASSED ALL REQUIRED MAINTENANCE TESTS.

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I WAS FOLLOWING INSTRUCTIONS GIVEN TO ME BY ACFT MAINT AND ENGINEERING AND PLANNING. I DID FOLLOW THE REQUIRED WRITE-UP OPS CHKS AND AGREED THAT THE VALVE NEEDED REPLACEMENT. I REMOVED AND INSTALLED THE VALVE SENT FOR THIS ACFT X WITHOUT INCIDENT. USING THE ACFT MAINT MANUAL; I ACCOMPLISHED THE OPS CHKS PER THE MAINT MANUAL PROCS AND THE SYS CHKED NORMAL ON GND AND THE EICAS MESSAGE CLRED. I RPTED IN TO WORK THE FOLLOWING DAY TO LEARN THAT THE ACFT HAD A REPEAT PIREP. UPON MY INVESTIGATION; I DETERMINED THAT AIRLINE MAINT AND ENGINEERING HAD PRODUCED THE WRONG PART NUMBER; WHICH MEANS THAT I THEN; IN FACT; HAD UNKNOWINGLY INSTALLED AN INCORRECT PART WHICH I BELIEVED CAUSED THE REPEAT PIREP AND ADDITIONAL MAINT ACTIONS. I FEEL THAT I AM DOING THE RESPONSIBLE THING BY FILING THIS RPT AS THIS WAS A MISTAKE ON MY PART; BECAUSE I SHOULD HAVE DOUBLECHKED THE PART NUMBERS TO THE VALVE THAT MY AIRLINE HAD SUPPLIED FOR THIS REPAIR. I HAVE LEARNED FROM THIS EXPERIENCE; THAT I SHOULD ALWAYS DOUBLECHK THE PART NUMBERS AND PARTS THAT MY AIRLINE SUPPLIES IN CASE THERE IS A MISTAKE. IN THE FUTURE; I'M CONFIDENT THAT MY ACTIONS WILL PREVENT THIS MISTAKE FROM EVER HAPPENING AGAIN. I WAS FOLLOWING THE INSTRUCTIONS OF AIRLINE MAINT AND ENGINEERING. I WAS GIVEN A WRITE-UP ORDER TO BITE CHK AND REPLACE THE OUTFLOW VALVE SENT AND ORDERED BY TECHNICIAN. USING THE MAINT MANUAL; THIS VALVE INSTALLED NORMALLY; TESTED NORMALLY.