sections this difference in number of sections and associated components as compared to fig1 makes no difference in the principle of the invention but somewhat simplifies the explanation thereof it should be understood that the principles hereafter explained would be applicable to a drum made up of any reasonable number of sections whether more or less than the drum 3 specifically illustrated as heretofore mentioned buffers 76 39 are piston cylinder units comprising cylinders 90 adapted to be supplied with compressed air the air comes from a pressure medium source not specifically shown in fig2 connected to a pressure medium supply line or conduit 91 containing a shut off means 92 and a pressure gauge 93 the air pressure is about 8 10 bars and can be adjusted by a pressure regulating valve on the shut off means 92 compressed air coming from conduit 91 travels through a solenoid valve 94 into a pressure medium pipe 95 and through a solenoid valve 94 39 into a pressure medium pipe 95 39 after leaving pipes 95 or 95 39 the compressed air travels through branch pipes 96 and 96 39 to a first group of cylinders 90 or a second group of cylinders 90 39 the adjacent cylinders in the first group being interconnected in the same manner as the cylinders 90 39 in the second group cylinders 90 i e the first group of piston cylinder units or buffers 76 39 are disposed along the left half of drum 3 whereas cylinders 90 39 are disposed along the right half of the drum the piston cylinder units are all identical so that not only the cylinders but also the associated pistons are of similar construction a lever 97 97 39 respectively is disposed at either.