Abstract: A one-way flap valve, particularly for induction pipes of cylinders of internal combustion engines of vehicles, comprising a number of modular passage units having substantially curved base walls and having internal dividers parallel to the side walls, capable of engaging frontally with flexible air-tight closure flaps to form air flow channels, said modular units are arranged in the pipe in various positions, with at least one of them having an outlet flow direction different from and convergent towards those of the other units, a distance piece having a profile curved according to the deformation curve of each flap of the adjacent units being placed between the unit with a different outflow direction and the adjacent unit.