Abstract: A sensor and powered valve actuator assembly adaptable to fit on and operate a manual valve, the sensor for detecting a valve operating trigger event such as a fluid leak, the actuator for automatically operating the manual valve in response to the triggering event. The assembly includes a motor, motor control circuit, operating shaft, and manual valve engaging member, in a housing mountable to a manual valve body. A sensor which may be remote to the housing is connected to the motor control circuit. When mounted, the valve engaging members extend from the shaft into flexible, rotational engagement with the manual valve shaft, such as with tines spanning or piercing the valve handle. The control circuit controls the motor based on a signal from the sensor, or other control means, such that the motor can actuate valve operation.