unit 65 are drawn within a line 30 components outside this are located on the fixed part 41 on the rotary part 40 are jaws 1 2 3 which are designed to grip and hold a pipe 70 as described above the jaws 1 2 3 are connected to the respective holding cylinder 1 a 2 a 3 a the piston sides of the cylinders 1 a 2 a 3 a are connected to respective valve assemblies 10 11 12 via respective connecting lines 1 b 2 b 3 b the valve assemblies 10 11 12 comprise a check valve 10 a 11 a 12 a that opens for hydraulic communication with the respective holding cylinder 1 a 2 a 3 a when the hydraulic fluid is at a certain pressure and stops communication in the opposite direction and the two way relief valve 10 b 11 b 12 b which is mentioned in connection with fig3 and which in a first position provides communication with the piston side of the respective holding cylinder 1 a 2 a 3 a and stops communication in the opposite direction and in a second position opens for communication both ways the respective check valve 10 a 11 a 12 a communicates with the piston side of a slave cylinder 18 via a respective line 10 c 11 c 12 c.