Actuator Explained: Types & Industrial Applications
An actuator is a device that converts an electrical, pneumatic, or hydraulic signal into physical motion. If sensors are the inputs to a control system, actuators are the outputs — motors, valves, cylinders, solenoids, contactors, dampers. Choosing the right actuator type for your application is one of the most consequential decisions in machine design.
Four power technologies
- Pneumatic — compressed air drives a cylinder or rotary actuator. Cheap, fast, simple, clean. Limited force per cylinder size; slow position control without proportional valves; air is "noisy" energy with low efficiency.
- Hydraulic — pressurised oil. Highest force-to-size ratio. Heavy machinery, presses, large excavators. Messier and more maintenance-intensive than pneumatic.
- Electric (motor) — AC motor with VFD or servo drive. Precise position/velocity control, clean, easy to integrate with PLC. Higher initial cost than pneumatic at small sizes.
- Electromechanical (solenoid, contactor) — electromagnetic force directly converted to short-stroke linear motion or contact closure. Used for valve solenoids, relay contactors, electromagnetic clutches.
By motion type
Linear actuators
- Pneumatic cylinders — air-driven linear motion. Fast, simple, common for clamping, indexing, pick-and-place.
- Hydraulic cylinders — high-force linear motion for presses, machine tools, excavators.
- Electric linear actuators — leadscrew or ball-screw driven by a stepper or servo motor. Precision positioning with feedback.
- Linear motors — direct-drive electric, no mechanical conversion. Sub-micron precision in semiconductor and printing equipment.
Rotary actuators
- AC induction motors — by far the most common rotary actuator in industry. Pumps, fans, conveyors, mixers.
- Servo motors — precision rotary positioning with encoder feedback.
- Stepper motors — open-loop precise rotary positioning at lower cost than servos.
- Pneumatic / hydraulic rotary actuators — vane or rack-and-pinion. Used for valve actuation in process plants.
Valve actuators
- Solenoid valve — direct-acting electric, on/off only.
- Pneumatic actuator + solenoid pilot — most common in process plants. Air-driven valve with electric solenoid controlling air supply.
- Electric actuators (Rotork, Auma, Limitorque) — motor-driven rotary actuators for large process valves. Position feedback, partial-stroke testing.
- Hydraulic actuators — for very large valves and high-pressure applications.
How to choose
- Force and stroke required — for small/medium loads, pneumatic and electric compete. For high force in compact form, hydraulic or large servo. For very small precise motion, electric/servo.
- Position control — pneumatic on/off is fine for clamping. Smooth motion control needs proportional pneumatic valves (expensive) or electric (more natural).
- Cycle rate — pneumatic excels at high-cycle short-stroke. Electric servos for repeated precision moves.
- Environment — washdown and clean rooms favour electric (no air contamination). Hydraulic ruled out for food and pharma.
- Energy efficiency — electric is most efficient. Compressed air loses ~80% of input energy; hydraulic 60-70%. For high-cycle applications, electric pays back.
- Safety — pneumatic valves can be safety-rated (pilot solenoid, redundant); electric drives now offer Safe Torque Off for SIL 3.
Frequently asked questions
What is an actuator?
An actuator is a device that converts an electrical, pneumatic, or hydraulic input signal into physical motion. Actuators are the output devices in a control system — motors, valves, cylinders, solenoids, contactors. They take commands from the PLC and produce mechanical action like opening a valve, moving a cylinder, or rotating a shaft.
What are the four types of actuators?
By power source: pneumatic (compressed air), hydraulic (pressurised oil), electric (motor-driven), and electromechanical (solenoid, contactor). By motion: linear (cylinders, leadscrews) and rotary (motors, vane actuators). Most industrial systems use a mix — pneumatic cylinders for fast clamping, electric motors for variable-speed processes, and hydraulic for high-force applications like presses.
What is the difference between an actuator and a sensor?
A sensor is an input device — it reads a physical quantity (temperature, pressure, flow, position) and sends an electrical signal to the PLC. An actuator is an output device — it receives an electrical signal from the PLC and produces physical motion or action (opening a valve, running a motor, energising a contactor). Sensors are the inputs; actuators are the outputs.
When should I use a pneumatic actuator vs an electric one?
Pneumatic excels at high-cycle short-stroke applications (clamping, indexing, pick-and-place) where simplicity, speed, and low initial cost matter. Electric actuators are better for precise position control, smooth motion, energy efficiency, and clean environments (food, pharma, semiconductor). For applications above 50,000 cycles/year, electric usually pays back the higher initial cost in energy savings.
What is a valve actuator?
A valve actuator is the device that opens and closes a process valve under PLC control. Common types: solenoid valves (small, direct-acting electric), pneumatic actuators with solenoid pilot (most common in process plants), motorised electric actuators (Rotork, Auma, Limitorque for large valves), and hydraulic actuators (for very large or high-pressure valves). Modern valve actuators often include position feedback, partial-stroke testing, and digital communication via HART or PROFINET.