US Patent 7270498 Flood vent

The flood vent has an elongated box-shaped frame having a top end, a bottom end including a floor, and opposing sidewalls that define a fluid passageway. The frame has an open front and a track formed in the rear of the frame. A door is slidably mounted in the track so that a normally closed position blocks the fluid passageway. The door is sufficiently buoyant to permit floodwater to float the door in the track and, thus, to automatically vent excess water through the fluid passageway. Installed in a crawl space, basement, or similar structure, the venting action of the flood vent limits hydrostatic pressure buildup against the walls of the structure when floodwaters rise, thus preventing structural damage from occurring.