A flapper valve assembly is provided for venting pressure in a tank. The flapper valve assembly includes a float assembly that is configured to be disposed within a valve housing. The float assembly may have a plurality of guide supports that extend from an end portion of the float assembly. A flapper member is movably supported on the float assembly. The flapper member may include a plurality of guide legs that correspond with the guide supports of the float assembly to maintain proper alignment of the flapper member relative to the float assembly.