Many I&C technicians who entered the trade halfway still feel lost about "what exactly goes on inside" after fixing electric valves a few times. When a newcomer asked for basic material in a peer community, senior engineers delivered a set of beginner explanations — organized here into a primer.
The power circuit chain: contactor closes (solid-state relay for higher demands) → motor turns → gear reducer multiplies torque → valve opens/closes.
- For forward/reverse motor control: the contactor scheme uses two contactors (one for open, one for close); a solid-state relay scheme needs only one;
- Two core setting groups: open/close position (travel cut-off) and open/close torque (torque cut-off) — commissioning is essentially tuning these two groups;
- Three common protections: over-current, motor over-temperature, and over-torque.
A modulating actuator is structurally similar to the on/off type, plus a servo amplifier to control the valve opening and a feedback unit (converting valve position into a 4–20 mA signal back to the control system), forming the command–feedback–motion closed loop.
In older plants, the hand operator, servo amplifier, and relays were separate devices — one actuator came with a whole cabinet of relays, complex wiring, and many failure points. Modern products integrate all of this inside the actuator body: today's "electric head" is already a complete control unit.
The seniors' advice was unanimous:
1. Learn to read the loop diagram first — once you can read it, electric valves hold no secrets;
2. Practice commissioning hands-on, and open the housing whenever possible to see the internals; competence grows with the number of faults handled;
3. Study the manuals — actuator manuals describe structure and setting methods in detail (the "Data Download" section of this site hosts the official manual compilation of major brands).
Electric actuators are not mysterious: on/off type = reversible motor + travel/torque cut-offs + three protections; modulating type adds the servo amplifier and the feedback loop. Hold onto this backbone, and any brand's manual and circuit diagram will fall into place much faster.
