Roof vent assembly for grain storage bin

A roof vent for a grain bin comprising:

• a housing defining a passageway adapted to communicate air flow between the interior of a grain bin and ambient air;
• a first flap closure means pivotally mounted within said housing on a horizontal axis above the center of gravity of said first flap closure means for substantially blocking solid matter from passing through said passageway when the air pressure differential between the interior of said grain bin and ambient air is insufficient to pivot said first flap closure means against the force of gravity and for pivoting and opening at least a portion of said passageway when the air pressure in said bin is sufficiently greater than the ambient air pressure to pivot said first flap closure means against the force of gravity;
• a second flap closure means pivotally mounted within said housing on a horizontal axis above the center of gravity of said second flap closure means for substantially blocking solid matter from passing through said passageway when the air pressure differential between the interior of said grain bin and ambient air is insufficient to pivot said second flap closure means against the force of gravity and for pivoting and opening at least a portion of said passageway when the air pressure in said bin is sufficiently less than the ambient air pressure to pivot said second flap closure means against the force of gravity;
• both of said first and said second flap closure means is of a curved airfoil shape;
• and
• both of said flap closure means being pivotally mounted to said housing along a substantially horizontal axis located from the bottom of respective ones of said flap closure means a distance at least sixty percent of the height and no greater than eighty percent of the height of respective ones of said flap closure means.