Electric Actuators

An electric actuator replaces the whole pneumatic chain — air supply, positioner, solenoid — with a motor, gearbox and control electronics. Where instrument air is absent, unreliable or expensive (remote wellheads, water plants, buildings), electric actuation is often the only sensible choice.

How they work

A reversible motor drives a multi-stage gearbox (spur or worm) into high torque at low speed. Travel is limited by torque-seating or limit switches; position control in modulating service comes from an internal electronic positioner receiving the 4–20 mA command — the electric equivalent of a pneumatic positioner.

Key sizing parameters

• Torque / thrust. For multi-turn and quarter-turn valves, required torque at seat and at mid-stroke; for linear globe valves with electric actuators, thrust through a stem nut conversion. Size against the valve's seating requirement with margin, as with pneumatic thrust.
• Duty cycle (ED%). The critical spec for modulating service. A 25% ED motor cannot chase a fast loop; frequent repositioning overheats the motor. Match the actuator's starts-per-hour and duty rating to the loop's actual movement demand.
• Stroking speed. Gear ratios trade speed for torque; check the travel time against your process requirement.
• Fail action. The classic weakness: a motor stops where it is. Fail-safe requires a battery backup, a capacitor-reserve drive, or a spring-return electro-hydraulic module — each adds cost and maintenance.

Electric vs pneumatic — the trade

• Electric wins on: no air infrastructure, high static thrust, precise modulating control, low stand-by losses, long cable runs.
• Pneumatic wins on: fast stroking, inherent fail action via spring or air failure, simplicity in hazardous areas, tolerance of frequent cycling, easy overload (a pneumatic actuator stalls without damage; a stalled motor cooks).