An actuator is one of the important components of an automatic control system. Based on the signal sent by the controller, it adjusts the value of the controlled object so that the controlled variable reaches or stays at the set value or within the set range. In other words, the controller is responsible for "judging" and the actuator for "acting" — however good the control strategy is, it ultimately has to be applied to the valve through the actuator.
By energy type, actuators can be divided into pneumatic, hydraulic, and electric. None of the three is absolutely superior; what matters is whether it matches the duty conditions. This article explains the features, limitations, and applications of the three types, and gives a selection judging order.
1. First, Be Clear: What the Actuator Does in the System
The actuator receives a control signal and outputs a linear displacement or an angular displacement to drive the controlled objects such as valves and dampers. Whether an actuator is easy to use is mainly judged by four things: whether the output force (torque) is sufficient, whether the action response is fast, whether long-term operation is stable, and whether maintenance and spare parts are convenient.
With different energy forms, the answers to these four things differ — which is also the fundamental reason why "on the same pipeline, some valves are pneumatic while others are electric".
2. Pneumatic Actuator: Simple Structure, Reliable Operation, Fire- and Explosion-Proof
A pneumatic actuator uses compressed air as its energy source, and has the advantages of a simple structure, reliable and steady operation, high output force, convenient maintenance, and fire- and explosion-proof performance, so it is widely used in production processes such as chemicals, paper, and refining.
It also has two easily overlooked advantages:
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It can be used together with passive instruments, mating directly in traditional pneumatic instrument systems without additional modification.
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Even when electric instruments or computer control are used, pneumatic actuators can continue to be used — through an electro-pneumatic converter or an electro-pneumatic valve positioner, the electrical signal is converted into a standard air pressure signal of 20–100kPa, and the pneumatic actuator is still controlled. That is, "computer control" and "pneumatic actuators" are not contradictory; adding a converter in between is enough to interface them.
Limitations: a reliable compressed air source is required; when the air supply contains water, oil, or impurities, the failure rate rises noticeably; the piping and accessories (filter, pressure reducing valve, solenoid valve) require matching investment.
3. Electric Actuator: Convenient Energy Availability, Fast Signal Transmission
The outstanding advantage of an electric actuator is convenient energy availability — electricity at the site is enough, and no air supply piping needs to be laid; at the same time, signal transmission is fast, interfacing directly with the control system, which facilitates remote, precise control and process data acquisition.
Limitations: complex structure and poor explosion-proof performance. A complex structure means many electrical and mechanical parts and increased failure points and maintenance difficulty; poor explosion-proof performance limits its use in flammable and explosive locations — in such places, an explosion-proof product is often chosen, or a pneumatic solution is used instead. In addition, the response speed of an electric actuator is constrained by the motor and reduction mechanism, and it is not necessarily advantageous under duty conditions requiring high-frequency, fast action.
4. Hydraulic Actuator: High Output Force, But Rarely Used in Production
A hydraulic actuator is rarely used in production processes such as chemicals and refining; its characteristic is high output force. Using hydraulic oil as the working medium, it transmits smoothly and has high stiffness, and it is advantageous only in special applications requiring extremely large thrust.
Limitations: it requires a hydraulic station and oil circuits, and the system is complex and takes up space; there is a risk of oil leakage, and high-temperature applications also need to consider oil temperature control; maintenance has high requirements for oil cleanliness. Therefore it is generally not chosen in routine process control.
5. The Three Actuator Types at a Glance
| Type | Energy | Main advantages | Main limitations | Typical applications |
|---|---|---|---|---|
| Pneumatic | Compressed air | Simple structure, reliable and steady operation, high output force, convenient maintenance, fire- and explosion-proof | Needs a reliable air supply; the failure rate rises when air quality is below standard | Process control in chemicals, paper, and refining, and flammable and explosive locations |
| Electric | Power supply | Convenient energy availability, fast signal transmission, easy remote precise control | Complex structure, poor explosion-proof performance | Locations with a power supply and low explosion-proof requirements |
| Hydraulic | Hydraulic oil | High output force, smooth transmission, high stiffness | Needs a hydraulic station and oil circuits, complex system, leakage risk | Special high-thrust applications; rarely used in chemical and refining processes |
6. How to Choose: Matching on 4 Dimensions
First dimension: explosion-proof and safety requirements. Flammable and explosive areas should give priority to pneumatic (fire- and explosion-proof); electric requires an explosion-proof model, with higher cost and maintenance requirements.
Second dimension: output force (torque) demand. For routine torque demand, either pneumatic or electric will do; only when extremely large thrust is required should hydraulic be considered.
Third dimension: control signal mode. When the system uses electric instruments or computer control and you wish to use a pneumatic actuator, fit it with an electro-pneumatic converter or an electro-pneumatic valve positioner to convert the electrical signal into a standard 20–100kPa air pressure signal; otherwise choose the corresponding actuator according to the system signal type.
Fourth dimension: site conditions and maintenance capability. Where there is a stable air supply and maintenance staff familiar with pneumatic parts, pneumatic is the most worry-free; where there is only a power supply, fewer pipelines are wanted, and fast signal transmission is required, choose electric; where neither condition is met, do not adopt hydraulic just for "high output force".
7. 5 Common Misconceptions
Misconception one: thinking electric is necessarily more advanced than pneumatic. In flammable and explosive locations, explosion-proof performance comes first, and pneumatic is often more suitable. Correct approach: look at the duty conditions first, then discuss the form.
Misconception two: looking only at the actuator body, not the supporting equipment. Choosing pneumatic yet ignoring air quality and the FRL configuration still means a high failure rate. Correct approach: consider air drying, filtration, and pressure reduction together.
Misconception three: computer control requires switching to an electric actuator. In fact, adding an electro-pneumatic converter or an electro-pneumatic valve positioner lets a pneumatic actuator also be computer-controlled. Correct approach: give priority to continuing with the existing actuator to reduce modification cost.
Misconception four: choosing hydraulic whenever large thrust is needed. Hydraulic is rarely used in chemical and refining processes, and in most duty conditions the output force of pneumatic is already sufficient. Correct approach: calculate by the actual torque demand and avoid oversizing.
Misconception five: the spare parts and maintenance methods of the three types are the same. The wearing parts and maintenance skills of the three are completely different. Correct approach: consider spare parts supply and maintenance capability together when selecting.
8. Review of the Three Actuator Types
The pneumatic actuator uses compressed air as its energy source and has a simple structure, reliable and steady operation, high output force, convenient maintenance, and fire- and explosion-proof performance; it is widely used in chemicals, paper, and refining, can work with passive instruments, and can also receive a standard 20–100kPa air pressure signal through an electro-pneumatic converter or an electro-pneumatic valve positioner. The electric actuator has convenient energy availability and fast signal transmission, but a complex structure and poor explosion-proof performance. The hydraulic actuator has high output force and is rarely used in production processes such as chemicals and refining.
The selection order can be summed up in one sentence: first look at explosion-proof and safety, then at torque demand, then match the signal mode, and finally compare site conditions and maintenance capability.
Conclusion
The three types of actuators correspond to three energy forms and three application boundaries: pneumatic wins on reliability and explosion-proof performance, electric wins on convenience and signal transmission, and hydraulic wins on output force. Putting duty-condition requirements first and brand and price later makes the chosen actuator both easy to use and easy to maintain. If you need pneumatic actuator selection advice or electro-pneumatic conversion and positioner matching solutions, please contact our service team.
Zhejiang Huaershi Auto-control Instrument Valve Co., Ltd.
Since 1989 · 30+ years focused on pneumatic actuators and pneumatic valves
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