An air-lock valve (1), especially for a band processing plant, provided for closing a gap-like opening (3), traversed by a flexible band substrate (4), between two different plant sections, featuring at least one moveable sealing body (7), cooperating with a sealing surface (5), when it closes said opening (3), and eventually said band substrate (4) is being firmly mounted between said body (7) and sealing surface (5) during the closing operation of said air-lock valve (1), is characterized, according to the invention, in that the sealing surface (5) surrounds opening (3) in frame-like fashion, and in order to close opening (3), said body (7) may be pressed in such a fashion upon sealing surface (5) and/or upon band substrate (4), traversing said opening (3), that it obstructs said opening (3) at least due to indirect juxtaposition at the edges of said sealing surface (5).