Abstract: An adaptor for manually operable lawn sprinkler control valves for converting such valves to automatic shut-off following a predetermined time interval. It comprises a rotatable shaft whose end portion is bifurcated to effectively grip the manual valve operator. A torsion spring and a rachet wheel or gear are fixed to the shaft, and a timer is provided having an arm for engagement with the rachet wheel. The shaft is manually turned to open the sprinkler valve, such motion storing energy in the spring but the timer arm prevents such energy from closing the valve. After a predetermined interval of time, the arm is moved out of engagement with the wheel and the torsion spring is permitted to return the sprinkler valve to closed condition.