Actuation & Instrumentation
Electric Actuator
An electric actuator uses a motor with a gear train to drive the valve stem or shaft, commanded by a control signal (4–20 mA with position feedback, or discrete open/close/stop contacts). Where instrument air does not exist or is expensive, electric actuation is the default.
Strengths: very high stiffness (holds position firmly against process forces), high available torque at low speed, precise positioning, easy integration with digital controls, and no air-quality dependency. Modern units include local controls, battery-backed fail action on some models, and complete diagnostics.
Trade-offs for throttling duty: motor duty cycling (a hunting controller will overheat the motor — sizing must consider starts per hour), lost-motion/backlash in gear trains contributing to dead band, and the absence of inherent fail-safe action unless spring-return or capacitor/battery mechanisms are specified. Cost is higher than pneumatic at small sizes.
Selection essentials: required torque/thrust including seat-load margin, modulating duty rating (S2/S4), power failure behaviour, and enclosure rating (IP67/68, hazardous areas).