Braking system using a valve

A system for blocking a plug valve, the system comprising:

• a plug that is movable in rotation about a longitudinal axis and that is rotatably connected to a valve body, the plug presenting a shaft extending along the longitudinal axis;
• and
• a blocker part mounted to be movable in translation along the longitudinal axis;
• wherein
• the plug presents an index portion comprising a first ramp and a second ramp, the two ramps being arranged around the shaft, extending in the same direction and having oppositely-handed slopes about the shaft;
• and
• the blocker part presents first and second index portions adapted to come selectively into contact with the first and second ramps, respectively;
• the blocker part being configured so as to be capable of being positioned selectively in:
• a free position, in which the blocker part is not in contact with the ramps of the plug;
• and
• a locking position in which the first and second index portions are respectively in contact with the first and second ramps, such that the first ramp (3) and the first index portion prevent the plug from turning about the longitudinal axis in a first direction of rotation, and the second ramp and the second index portion prevent the plug from turning about the longitudinal axis in a second direction of rotation, opposite to the first direction of rotation.