US Patent 7169202 Filter assembly

A filter assembly includes a reusable filter frame and a replaceable, pleated, reversibly expandable, self-spacing filter removably arranged in the frame. The self-spacing pleated filter expands uniformly with equal pleat spacing to allow the filter to be easily installed in the reusable filter frame without the aid of a secondary spacing structure. When the filter is expanded to the length of the filter frame, the filter is under tension, thereby allowing the length of the filter to be readily adjusted to match the length of the frame and allowing the pleats to be aligned with corresponding ribs provided in the frame.