A valve, e.g. of an aircraft drinking water system, has a rotatable adjusting shaft to adjust the valve between its open end position and its closed end position. A mechanism for operating the adjusting shaft includes a push-pull cable connected to a toothed rack that engages a toothed gear element secured to the adjusting shaft. The mechanism converts the push-pull linear motion of the cable to a reciprocating rotational motion of the adjusting shaft. End sections of the rack and the gear element have no gear teeth, so the rack automatically disengages from the gear element once the end position of the valve is reached. The disengaged rack can slide beyond the stopped end position of the gear element, and re-engages with the gear element once it slides back into the operating range. The valve cannot be forced beyond its end positions, despite excessive input motion of the cable.