selfactuated

Selfactuated, often written self-actuated, describes devices or systems that operate automatically using their own internal energy source or the energy contained in the process they control, rather than through external actuation or operator input. In engineering and process control, self-actuation relies on physical properties such as pressure, temperature, differential pressure, or fluid flow to drive movement or regulation.

Common self-actuated devices include pressure-relief valves that open when inlet pressure exceeds a fixed setting, pressure-reducing or back-pressure regulators that maintain a chosen downstream pressure, and thermostatic or thermal valves that respond to temperature with a sensing element and a movable valve seat. Other examples are self-actuated level controllers and flow control devices that use buoyancy, gravity, or differential energy to regulate.

Applications span chemical processing, oil and gas, power generation, HVAC, and water treatment, where reducing reliance on external controls can improve reliability and safety. These devices tend to be compact, require less power, and are often intrinsically fail-safe; however, they must be properly specified for set-point accuracy, response time, hysteresis, and material compatibility. Routine maintenance and calibration are important to counter drift and fouling.

Differences from externally actuated systems are key: self-actuated devices respond directly to process variables without pilot lines, wiring, or electric actuation. They are sometimes complemented by pilot-operated or electronically controlled systems when more complex control is required.

See also: actuators, automatic control, pressure relief valve, regulator, thermostatic valve, pilot-operated valve, safety valve, passive control.