Patent attributes
A collapsible ladder includes two vertical stiles with rungs disposed therebetween. Each stile is formed by a plurality of telescopically collapsible columns. Each collapsible column has a bottom opening, an inner wall and a cover to cover the bottom opening. The cover has a small cylindrical portion and a large cylindrical portion with a peripheral surface located under the small cylindrical portion. The small cylindrical portion is inserted into the bottom opening of a column The large cylindrical portion is exposed outside of the column and inserted inside of a next lower column. A sealing ring is disposed inside a annular groove and touches the inner wall of the next lower column when the stile is extending or collapsing. One or more air ducts are provided in the cover. A first air opening iarranged above the large cylindrical portion in correspondence with an opening in a lower wall part of the column.
