Abstract: A door having a leaf of flexible material and held in suspension for raising and lowering within an opening has two lines attached to the lower portion of the door leaf, one line at each of its ends. The lines are also connected to a hoist means. The ends of the door leaf are guided in U-shaped forms having lateral flanges, the flanges being attached to the vertical defining surfaces of the door opening and each form carries one of the lines that extends to the hoist means. Each line is connected to its respective end of the door leaf by an intermediate release and lock means which responds to a predetermined decrease in load on the respective line to lock and hold fast the door leaf against the lateral flanges of the respective U-shaped form in any position along the door's vertical path of movement.