may be effected by cotter pins longitudinal pins etc inthe case shown two longitudinal pins 12 have been illustrated the lever 11 comprises a second free end 113 supporting a fixed shaft 13 around which a roller 14 is mounted to roll freely it is observed in fig4 thatthe roller 14 lies exactly opposite the edge or ramp 91 of each tab 9 being given as explained hereinabove that the guide vanes 7 tend to close i e adopt the positions illustrated in fig3 under the hydrodynamic effects or the like in the closed state the ring 1 lies in an angular position in which the ramps 91 are in abutment on the rollers 14 but without acting thereon when it is desired to open the distributor the ring 1 is displaced angularly in the direction of arrow f so that the ramps 91 on acting on the rollers 14 cause the angular displacement of the guide vanes 7 when it is desired to close the distributor it suffices to return the ring1 rearwards and the efforts which load the guide vanes displace the latter and take them into the position of fig3 in the event of a mishap i e when an obstacle engages between two guide vanes when the distributor is open if a need for closure becomes apparent the ring 1 will be turned in the direction opposite that of arrow f with the result that all the rollers will continue to cooperate with the ramps except the one which corresponds to the jammed guide vane of which the end 113 of the lever will be housed.