cylinder where said first piston rod is guided via the first piston part and by means of a seal 9 arranged at the lower end of the cylinder the first piston rod 8 is supported by means of a through hole 10 in one of its ends on a journal fastened to the mounting and not shown in the figure while said cylinder 6 on its outside supports a bearing housing 12 provided with a bearing journal 11 see fig4 c the bearing journal 11 is assumed to coact with a supporting hole arranged in the barrel and not shown in detail the bearing housing is attached to the cylinder via a spherical bearing comprising an upper member and a lower member the higher member designated by numeral 13 which is protected from contamination by means of a rubber sleeve 14 said first piston part 7 and first piston rod 8 are also tubular a second piston part 15 is supported inside the first piston rod 8 and a second piston rod 16 belonging to the second piston part extends inside the first piston rod 8 and the first piston part 7 the second piston rod is moreover fastened to the upper end surface of the cylinder 6 in the fastening device 17 through a special insert unit 18 parts of the first piston part 7 and the first piston rod 8 are made double walled and.