further to a second gear wheel 25 meshing with a second toothed rim 26 attached to the rotary end piece 4 the gearing 23 24 serves to reverse the rotational direction of the gear wheel 25 in relation to the gear wheel 21 the gear wheels of the gearing 23 24 are of equal size and give therefore no change of speed when the motor 14 rotates the end piece 5 rotates in the same rotational direction as the motor 14 the end piece 4 rotating in the opposite rotational direction the positioning of the components of the transmission in relation to the shaft 9 is shown as seen from the end piece 4 in fig4 and as seen from the end piece 5 in fig5 fig6 shows an alternative transmission having two electric motors 27 28 each carrying a gear wheel 29 30 each driving a toothed rim 22 26 with separate speed control of the motors 27 and 28 the number of revolutions per minute of the end pieces 4 5 may individually adjust itself to the internal pipe circumference against which the respective wheels 7 rest see fig1 the pipe tractor 2 may be imagined used for operations wherein the intermediate section 3 with the cover 17 advantageously may rotate while the pipe tractor 2 is running such rotation of the intermediate section 3 can be achieved by giving the end piece 4 and the end piece 5 different transport speeds e g by giving the motors 27 28 different numbers of revolutions per minute and the intermediate section 3 will then rotate with a speed proportional with the.