annular spacer 49 which joins the stators 25 and 28 and surrounds the rotors 26 and 27 according to the invention pressure equilibrating or pressure balancing channels 50 51 in which no liquid circulates are provided in at least one of the rotors the rotor 27 in the example shown in fig1 to 10 for maintaining a pressure equilibrium the channels 50 emerge fig2 through the right hand face of the rotor 27 in an occluded region 52 of the stator 28 that is to say a region with no outlet a solid wall in the example shown and through the left hand face of the rotor 27 in the slots 45 in the plate 26 for return to the reservoir 17 the channels 51 also emerge fig2 through the right hand face of the rotor 27 in an occluded region 53 of the stator 28 a solid wall in the example shown and through the left hand face of the rotor 27 in slots 46 in the plate 26 for return to the reservoir 17 the equilibration channels 50 and 51 are independent of the circulation passages 43 and 44 by virtue of the channels 50 and 51 total or partial equilibrium of the pressures is achieved and this makes it possible to avoid the use of bearings for taking up an axial thrust if the driver does not turn the steering wheel 12 the parts 13a and 13b are kept in the rest position by means of the torsion bar 33 fig8 and 10 show how the various passages and grooves are.