The valve has a passage that is partially closed by torsion deformation of a flexible portion (1) of the wall of the passage. An actuation unit actuates in rotation a movable end (3) of the flexible portion and includes a cable transmitting movement to the end of the flexible portion. The cable has an end fixed to a gripping unit (14) and another end fixed to a groove of a rotating shaft. A pulley (12) deviates the cable. An independent claim is also included for a surgical or medical instrument comprising a valve.
