Abstract: A compressed air dehumidifier comprises two containers having an adsorbent therein and having connections for the supply and delivery of air. Valve structure are provided for connecting the containers alternatingly one at the time into a compressed air system for passing air to be dehumidified through the connected container. Apparatus is provided for choked bleeding of a fraction of the dehumidified air from the connected container to the other container. A control valve (16-19) for accomplishing said alternatingly connection and for discharging said air fraction from said other container to the surrounding air includes a valve body (19), which has two recesses (37) for locking engagement one at the time with an axially movable valve stem (26) in order to hold the valve body against either one of two seats (16, 17), between which the valve body is movable.