The Index explains that the turning action is normally for twisting stuff:
Turning is the act of rotating something - say, a dial.
In the Standard Rules there are no carry out rules for this action because nothing in the standard Inform world model which reacts to it. The action is provided for authors to hang more interesting behaviour onto for special cases: say, turning a capstan.
You can easily redirect ‘turning the valve’ to ‘turning the valve off and on,’ but the action for ‘turning [off or on]’ is ‘switch.’ Like so:
Instead of turning the valve:
if the valve is switched off:
try switching on the valve;
otherwise:
try switching off the valve.