Typically, electric actuators are used in industrial applications to control positioning of devices, such as valves, gates, or the like. In chemical, petroleum, gas, and related industries, actuators are employed for controlling the flow of liquid from one location to another. For example, in boilers related applications, stem flow to a turbine may be controlled through a flow control valve. In certain situations, flow of hazardous chemicals may be controlled from one location to another. In such applications, it may be necessary to terminate fluid flow in emergency situations, such as the loss of electrical power, in order to prevent loss of fuel and/or the undesirable effects of contamination or pollution.
Actuator technologies can be designed with a fail-safe feature upon power loss. Fail-safe features in an actuator can be activated when power loss or other external failure condition causes the actuator to move the valve to a pre-determined position, without benefit of external electric power. Fail-safe actuation has been approached in several ways. Some approaches involve energy storage techniques, such as a spring that is used to move a valve or a damper to a certain pre-determined position, such as a closed position. For example, in U.S. Pat. No. 6,431,317, a fail-safe actuation approach includes a transmission and cam-clutch system used to transmit a potential energy stored in the spring to achieve a desired output. However, such a transmission system occupies high volume, requires high torque, is complex, and susceptible to failure.