What was found
THE CHECK VALVE IS TO PREVENT FUEL IMBALANCE WING TO WING. WHEN CHECK VALVE IS OPERATING CORRECTLY IT IS DIRECTING FUEL FROM ONE SIDE FUEL STORAGE/DISTRIBUTION DIRECTLY TO THE OPPOSITE ENGINE. A FUEL IMBALANCE CONDITION WAS NOTED WHILE THE AIRCRAFT WAS IN MAINTENANCE. FURTHER INVESTIGATION FOUND THAT THE ROLL PIN RETAINING THE FLAPPER VALVE HAD MIGRATED OUT SLIGHTLY AND LODGED IN SUCH A WAY THAT IT BOUND UP THE FLAPPER VALVE PREVENTING IT FROM CLOSING. A NEW VALVE WAS ORDERED AND WHEN IT WAS RECEIVED THE ROLL PINS WERE ALSO FOUND TO BE FREE-FLOATING, APPARENTLY BY DESIGN. THE POTENTIAL RISK FOR THIS DESIGN IS THAT BECAUSE THE ROLL PINS DO NOT APPEAR TO BE SECURE, THERE IS A RISK THAT THE PINS WILL MIGRATE OUT AND BIND THE FLAPPER VALVE, PREVENTING IT FROM CLOSING.