Abstract: Apparatus operating by means of compressed air, comprising a displaceable cylinder, open at both ends, in which there bears a displaceable piston designed for expulsion of fixing elements fed forward below the piston. The cylinder and the piston are displaceable, by the action of air, in a cylinder housing between an upper and a lower end position at which are arranged damping elements. The cylinder and the piston bear with their respective and faces at their respective end positions against a surface of the damping element. The apparatus comprises an inlet and an outlet for the air, the flow of which is controlled by means of a valve, and an upper chamber and a lower chamber. These chambers are in connection with the inside of the cylinder by means of at least one opening in the cylinder wall. Furthermore, the apparatus comprises at least one second opening in the cylinder wall which is in connection with the outlet via a return channel depending on the position of the cylinder.