A B757-200 ACFT MAINT TECH REPORTS OF FINDING A B757 WITH MASKING TAPE INSTALLED OVER ALL FOUR FLAPPERS FOR THE OVERPRESSURE RELIEF VALVES. ACFT WAS RECENTLY PAINTED.

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ALL FOUR FLAPPERS FOR OVERPRESSURE RELIEF VALVE HAS MASKING TAPE INSTALLED BLOCKING ALL FOUR VENT HOLES. TAPE WAS INSTALLED FROM UNDER FLAPPERS. TAPE WAS PAINTED COLOR #1 THROUGH VENT HOLE. VALVES STUCK SHUT FROM PAINT. COLOR #2 EDGE BAND OF FLAPPERS HAD COLOR #1 OVERSPRAY ON THEM. THIS IS THE SAME CONDITION AS ACFT Y. BOTH ACFT HAD NEW PAINT COLORS. IN BOTH CASES IT APPEARS TAPE WAS INSTALLED WHEN ACFT PAINTED BUT WAS NEVER REMOVED BY VENDOR PAINTING COMPANY.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THIS WAS THE SECOND ACFT HE FOUND THAT HAD BEEN FLYING AROUND WITH MASKING TAPE COVERING THE FLAPPERS AFTER BEING REPAINTED. THESE FLAPPERS WERE ALSO BASICALLY GLUED SHUT FROM THE EPOXY PAINT THAT WAS APPLIED TO THE FUSELAGE. THESE ARE THE POSITIVE PRESSURE RELIEF VALVES AND THE B757 HAS TWO OF THEM APPROX MID WAY UP THE FUSELAGE JUST AFT OF THE LEFT WING INBOARD TRAILING EDGE. EACH VALVE HAS TWO FLAPPERS THAT OPEN OUTWARD WHEN CABIN INTERNAL PRESSURIZATION EXCEEDS DIFFERENTIAL LIMITS. REPORTER ALSO STATED THAT HIS CARRIER HAS RESTRICTED THE MECHANICS' ABILITY TO LOOK BACK INTO THE MAINT HISTORY OF THEIR ACFT. MANY OF THESE PAINT JOBS ARE DONE ON WORK CARDS AND ARE NOT GENERALLY VISIBLE IN THE MAINT DATABASE AVAILABLE TO MECHANICS. HE KNOWS THIS SECOND ACFT HAD BEEN FLYING AT LEAST THIRTY DAYS WITH THE MASKING TAPE OVER THE POSITIVE PRESSURE RELIEF VALVES.