In modern industrial automation systems, valves serve as critical components for controlling the flow, pressure, and direction of liquids, gases, steam, and other process media. However, the performance of a valve depends not only on its design and materials but also on the actuator responsible for driving its operation. Among various actuator technologies available today, electric actuators have become increasingly popular due to their precision, reliability, energy efficiency, and compatibility with advanced automation systems.
Selecting the correct electric actuator for a control valve is a key decision that directly affects system performance, operational safety, energy consumption, and maintenance costs. An incorrectly sized or unsuitable actuator can lead to poor valve performance, excessive wear, increased downtime, or even complete process failure. Therefore, engineers and plant operators must carefully evaluate application requirements before choosing an actuator solution.
Electric actuators are widely used across industries such as oil and gas, chemical processing, power generation, water treatment, pharmaceuticals, food and beverage, and industrial manufacturing. They provide accurate valve positioning, intelligent control capabilities, and seamless integration with distributed control systems (DCS), programmable logic controllers (PLC), and industrial communication networks.
Among the different types of electric actuators, two major categories dominate industrial valve applications: multi-turn electric actuators and linear output electric actuators. Although both convert electrical energy into mechanical movement, their operating principles, applications, advantages, and limitations are different.
This guide provides a comprehensive overview of electric actuators, explains the essential factors to consider during selection, and compares multi-turn and linear output electric actuators to help users choose the most suitable solution for their control valve applications.
An electric actuator is a mechanical device that converts electrical energy into controlled mechanical movement to operate a valve. It typically consists of an electric motor, gearbox, drive mechanism, control module, position sensor, and protective housing. When an electrical signal is received from a control system, the motor generates rotational force, which is converted into either rotary or linear motion to move the valve stem or operating shaft.
Compared with pneumatic and hydraulic actuators, electric actuators offer several advantages. They do not require compressed air systems or hydraulic power units, reducing infrastructure requirements and operating costs. They also provide highly accurate positioning control, making them suitable for applications where precise flow regulation is required.
Modern electric actuators are often equipped with intelligent features, including:
- Digital position feedback
- Remote monitoring capabilities
- Fieldbus communication protocols
- Self-diagnostic functions
- Torque protection
- Automatic calibration
- Emergency operation functions
These advanced features allow electric actuators to support smart factory initiatives and Industry 4.0 automation strategies.
However, choosing an electric actuator is not simply a matter of selecting a model with sufficient power. Engineers must consider several technical parameters, including valve type, operating torque, thrust requirements, environmental conditions, power supply, and control system compatibility.
The first and most important consideration is the type of valve being operated. Different valves require different types of mechanical movement, which determines whether a rotary or linear actuator should be selected.
Industrial valves can generally be divided into two categories according to their operating motion:
Rotary valves require the valve stem or shaft to rotate to achieve opening and closing. Common examples include:
- Ball valves
- Butterfly valves
- Plug valves
These valves usually require quarter-turn or multi-turn rotary actuators depending on the valve design.
For example, a butterfly valve typically rotates 90 degrees between fully open and fully closed positions, making it suitable for quarter-turn electric actuators. A large ball valve, however, may require higher torque output due to pipeline pressure and sealing forces.
Linear valves operate by moving the valve closure element up and down along a straight path. Typical examples include:
- Globe valves
- Gate valves
- Diaphragm valves
- Control valves
These applications usually require linear output actuators or multi-turn actuators combined with linear conversion mechanisms.
Choosing an actuator that matches the valve motion is essential. Using an unsuitable actuator can result in insufficient valve travel, inaccurate positioning, excessive mechanical stress, or premature failure.
One of the most critical factors in actuator selection is determining the required operating force.
For rotary valves, the required force is measured in torque, usually expressed in Newton meters (Nm). Torque requirements depend on several factors:
- Valve size
- Pressure differential
- Sealing design
- Operating frequency
- Fluid characteristics
- Valve friction
For example, a large diameter ball valve installed in a high-pressure pipeline may require significantly higher torque than a small butterfly valve operating under low-pressure conditions.
For linear valves, the required force is measured as thrust, usually expressed in Newtons (N) or kilonewtons (kN). Thrust requirements are influenced by:
- Stem diameter
- Differential pressure
- Packing friction
- Valve plug design
- Required shutoff force
Selecting an actuator with insufficient torque or thrust may prevent the valve from fully opening or closing. On the other hand, oversizing an actuator can increase equipment costs and create unnecessary mechanical stress.
Therefore, accurate actuator sizing should always be based on manufacturer calculations and actual operating conditions.
Industrial environments can be extremely challenging, and electric actuators must be designed to withstand specific operating conditions.
Important environmental factors include:
Different applications may expose actuators to extreme temperatures. For example:
- Power plants may involve high-temperature steam systems.
- Chemical plants may operate in heated processing areas.
- Outdoor installations may experience freezing conditions.
The actuator must have a suitable temperature rating to ensure reliable performance.
Outdoor installations, wastewater facilities, and marine environments require actuators with appropriate protection levels.
Ingress protection ratings such as IP65, IP67, or IP68 indicate resistance against dust and water penetration.
Industries involving chemicals, saltwater, or aggressive gases require actuators with corrosion-resistant housings and protective coatings.
In oil, gas, and chemical industries, actuators may need explosion-proof certification to prevent ignition risks in areas containing flammable gases or vapors.
Selecting an actuator designed for the actual working environment improves service life and reduces unexpected failures.
Modern industrial facilities rely heavily on automated control systems, making actuator compatibility an essential consideration.
Electric actuators can support various control methods:
On/off actuators are designed for simple opening and closing operations. They are commonly used for isolation valves where only two positions are required:
- Fully open
- Fully closed
Modulating actuators provide continuous valve positioning, allowing operators to adjust flow rates precisely.
They are widely used in:
- Process control systems
- Temperature regulation
- Pressure control applications
- Flow management systems
For advanced automation applications, actuators may support communication protocols such as:
- Modbus
- Profibus
- Foundation Fieldbus
- HART
- Industrial Ethernet
Integration capabilities allow operators to remotely monitor valve position, diagnose problems, and optimize process performance.
A multi-turn electric actuator is one of the most widely used actuator types in industrial valve automation. As its name suggests, this actuator produces multiple rotations of the output shaft to fully open or close a valve. The actuator transfers rotational torque through a gearbox mechanism, allowing the valve stem to move through multiple turns.
Multi-turn electric actuators are primarily designed for valves that require rotational movement combined with linear stem travel. They are commonly paired with rising stem valves, including gate valves and globe valves, where the valve requires several rotations of the stem to reach the fully open or fully closed position.
Unlike quarter-turn actuators, which rotate only 90 degrees, multi-turn actuators can provide continuous rotation and high torque output. This makes them particularly suitable for large industrial valves installed in demanding applications where reliable shutoff and precise positioning are required.
These actuators usually include an electric motor, reduction gearbox, torque switch, limit switch, manual override mechanism, and electronic control unit. Advanced models may also include digital displays, remote communication interfaces, and intelligent diagnostic systems.
Gate Valve Applications
Gate valves are among the most common applications for multi-turn electric actuators.
Gate valves are primarily used for isolation purposes in industries such as:
- Oil and gas transportation
- Water distribution systems
- Power generation
- Chemical processing
- Mining operations
Because gate valves require the gate plate to travel vertically through a significant distance, multiple rotations are needed to move the stem. A multi-turn actuator provides the necessary torque and precise movement required for reliable operation.
In large pipeline systems, manually operating gate valves can be time-consuming and inefficient. Electric actuation allows operators to control valves remotely, improving safety and reducing labor requirements.
Globe Valve Applications
Globe valves are widely used for flow regulation because of their excellent throttling capability. They require accurate positioning of the valve plug to control flow rates.
Multi-turn electric actuators are commonly used with globe valves because they provide:
- Accurate stem movement
- High positioning accuracy
- Reliable shutoff capability
- Stable flow control
In applications such as steam systems, cooling water systems, and chemical processing lines, precise actuator control helps maintain stable process conditions and improves energy efficiency.
One of the primary advantages of multi-turn electric actuators is their ability to generate high torque output.
Large industrial valves often experience significant resistance caused by:
- High pipeline pressure
- Large sealing forces
- Heavy valve components
- Fluid friction
Multi-turn actuators use gearbox systems to multiply motor torque, allowing them to operate large valves effectively.
Multi-turn actuators provide excellent positioning accuracy, making them suitable for applications requiring controlled valve movement.
With integrated position sensors and digital control systems, operators can accurately monitor valve position and adjust flow conditions.
This capability is especially valuable in:
- Process industries
- Power plants
- Chemical facilities
- Automated production systems
Industrial environments often require equipment that can withstand continuous operation under demanding conditions.
Multi-turn electric actuators are designed with:
- Strong mechanical structures
- Weather-resistant housings
- Thermal protection systems
- Torque limiting devices
These features improve reliability and reduce unexpected downtime.
Despite their advantages, multi-turn actuators also have some limitations.
Because they contain powerful motors and reduction gear systems, multi-turn actuators are generally larger and heavier than simpler actuator types.
This may create challenges when:
- Installation space is limited
- Valve access is restricted
- Structural support is insufficient
Engineers must consider mounting requirements before installation.
Multi-turn actuators contain more mechanical components compared with some linear actuator designs.
Additional components may include:
- Multiple gear stages
- Drive sleeves
- Bearings
- Mechanical limit systems
Although modern designs have improved reliability, regular inspection and maintenance may still be required to ensure long-term performance.
Linear output electric actuators are designed to produce straight-line movement rather than rotational motion. The actuator converts electrical energy into linear thrust, moving the valve stem directly in a vertical or horizontal direction.
These actuators are especially suitable for control valves where precise stem positioning is required.
Unlike multi-turn actuators, linear output actuators do not rely on rotational movement to operate the valve. Instead, they typically use mechanisms such as:
- Ball screw drives
- Lead screw systems
- Electric motors with linear conversion mechanisms
Their compact design and direct motion characteristics make them increasingly popular in automated process control applications.
Globe Control Valves
Globe control valves are among the most common applications for linear electric actuators.
In automated process systems, globe valves regulate:
- Flow rate
- Pressure
- Temperature
- Fluid level
The actuator must accurately adjust the valve plug position according to signals from the control system.
Linear output electric actuators provide excellent positioning accuracy, making them suitable for demanding process control environments.
Typical applications include:
- Chemical plants
- Pharmaceutical production
- Food processing facilities
- Heating and cooling systems
Gate Valve Applications
Although multi-turn actuators are traditionally used for gate valves, certain gate valve designs can also utilize linear electric actuators.
These applications are often found where:
- Fast response is required
- Installation space is limited
- Direct stem movement is preferred
Diaphragm Valve Applications
Diaphragm valves require precise linear movement because the diaphragm must move directly against the valve seat.
Linear electric actuators are commonly used in industries requiring strict hygiene standards, including:
- Pharmaceutical manufacturing
- Biotechnology
- Food and beverage processing
Their accurate movement capability helps maintain sanitary operation and prevent contamination risks.
The greatest advantage of linear electric actuators is their direct movement.
Because the actuator output matches the valve movement direction, the mechanical structure is simplified.
Benefits include:
- Accurate positioning
- Fast response
- Reduced mechanical losses
- Improved control performance
Compared with many multi-turn actuators, linear output actuators typically have a more compact structure.
This makes them suitable for:
- Small equipment installations
- Modular systems
- Space-limited industrial facilities
Their smaller footprint can simplify installation and reduce supporting structure requirements.
The simplified mechanical design of linear actuators means fewer moving parts.
Compared with complex gearbox-driven systems, they may require:
- Less lubrication
- Fewer mechanical inspections
- Reduced maintenance downtime
This can help improve overall system reliability.
The biggest limitation of linear actuators is that they are designed only for linear motion applications.
They cannot directly operate rotary valves such as:
- Ball valves
- Butterfly valves
- Plug valves
unless additional conversion mechanisms are installed.
Although modern linear electric actuators can generate significant thrust, many models are designed for smaller or medium-sized valves.
For extremely large industrial valves requiring very high operating force, hydraulic or specialized multi-turn systems may still be preferred.
Before selecting an actuator, engineers should collect essential application information, including:
- Valve type
- Valve size
- Operating pressure
- Media characteristics
- Required operating frequency
- Control method
- Environmental conditions
A complete understanding of the application ensures proper actuator selection.
The actuator must match the valve’s operating principle.
For example:
- Gate valves → Multi-turn electric actuators
- Globe valves → Multi-turn or linear actuators depending on application
- Control valves → Linear output electric actuators
- Butterfly valves → Rotary electric actuators
Selecting the correct actuator type prevents operational problems and improves valve performance.
Actuator sizing should always consider actual operating conditions.
Important parameters include:
- Maximum differential pressure
- Valve friction
- Safety factor
- Required operating speed
Oversized actuators increase investment costs, while undersized actuators may fail during operation.
Electric actuators are available with different voltage options, including:
- 24V DC
- 110V AC
- 220V AC
- 380V AC
The selected actuator must match the facility’s electrical infrastructure.
Incorrect power compatibility can result in malfunction or equipment damage.
Modern automation systems require intelligent actuator functions.
Important features include:
- Remote control
- Digital position feedback
- Alarm indication
- Communication protocols
- Self-diagnostics
These capabilities improve operational efficiency and allow predictive maintenance.
Selecting the right electric actuator is essential for achieving reliable, efficient, and precise valve control in industrial automation systems. The decision should be based on valve type, torque or thrust requirements, operating environment, power supply, and control system compatibility. Multi-turn electric actuators are ideal for applications requiring high torque and rotational movement, such as gate and globe valves, while linear output electric actuators provide accurate direct motion for control and diaphragm valves. By carefully evaluating application requirements and actuator characteristics, industries can improve process performance, reduce maintenance costs, and ensure long-term operational reliability.
