a process and a device for cleaning inner or outer walls of vertically extending or inverted tubes of heat exchangers and especially for cleaning tubes in trash incinerators . the process involves imparting kinetic energy to the tubes in an axial direction and then suddenly stopping the tubes to shake loose dirt and the like . the device for the process includes arranging a plurality of rows of vertically extending tubes such that the tubes move upwardly and downwardly in the direction of the axis of the tubes . the tubes advantageously include their own lower distributors and upper headers . these distributors and / or headers rest on a movable cam or cam plate which , for example , may be rotated so that a radially extending offset of the shoulder of the cam permits the cam to lift the upper headers upwardly to a height at which point they are suddenly dropped . in an alternative embodiment , the upper header tubes are raised or lifted at their ends by a pneumatic or hydraulic piston cylinder , and the tubes are then lowered by the acceleration of gravity .