A pressure device for machines for dewatering or filtering of suspensions, sludges or the like or for material to be pressed for the exertion of surface pressure on at least one circulating pressure belt which can be provided for supporting an equally circulating filter belt, which pressure device consists of an essentially completely hollow pressure bladder in the form of a closed frame in particular of essentially quadrangular shape viewed in top view of the pressure belt, which pressure bladder is subjectable to pressure medium and forms a very small, self-adjusting gap on the edge.