cooperation of the pins 46 1 and 46 2 and of the grooves 72 1 and 72 2 prevents a separation of the nozzle 1 and of the adaptor 4 when the valve 50 is detached from the convergent part 22 a in effect when the pin 63 slides in the part 71 a of the notch 71 the pins 46 1 and 46 2 may slide in the parts 72 a 1 and 72 a 2 of the grooves 72 1 and 72 2 on the other hand when the heels 44 and 45 push the lever 60 as represented by arrow f 5 in fig3 the pivoting f 4 of the rocker 40 has the effect of taking pins 46 1 and 46 2 in the parts 72 b 1 and 72 b 2 of the notches 71 1 and 72 2 due to the displacement of the trigger 70 under the effect of the effort f 7 the pins 46 1 and 46 2 then each slide along a lateral surface 72 c 1 72 c 2 respectively of the notches 72 1 and 72 2 the pins 46 1 and 46 2 are in that case in abutment against the surfaces 72 c 1 and 72 c 2 with the result that the rocker 40 can no longer pivot about axis y 1 y u2032 1 in a direction opposite to arrow f 4 the rocker 40 thus being locked by its cooperation with surfaces 72 c 1 and 72 c 2 in a configuration where its pins 46 1 and 46 2 are lowered it exerts on the rod 30 an effort.