Linear Electric Actuator

A linear actuator is an electromechanical device that generates linear motion of a stem and is primarily used as an electric actuator for control valves. Its main function is precise valve positioning, smooth flow control, and automation of control valves within industrial process automation systems (PLC/SCADA). Unlike quarter-turn or multi-turn actuators, a linear actuator does not rotate the valve stem but raises and lowers it to a specified position with accuracy down to fractions of a millimeter. This is the fundamental mechanism for regulating flow in industrial pipeline systems.

Our website features electric actuators for control valves, ranging from compact models to heavy-duty actuators designed for large-diameter control valves used in the oil & gas, power generation, and process industries.

How a Linear Electric Actuator Works

A control valve electric actuator consists of three main components: an electric motor, a gearbox with a mechanism that converts rotary motion into linear motion (ball screw, lead screw, or rack-and-pinion drive), and an output stem connected to the valve stem. A control signal is sent to the actuator, the motor rotates the screw through the gearbox, the screw moves the nut, the nut pushes or pulls the stem, and the valve changes its position.

The key difference from other types of electric actuators lies in the operating mode:

• On/Off Mode (Open / Close) – the simplest operating mode, where the valve moves only between its fully open and fully closed positions.
• Modulating Control Mode – the primary operating mode for linear actuators. A 4–20 mA input signal determines the exact stem position with an accuracy of up to 1% of the full stroke, allowing the actuator to hold the valve at any intermediate position for smooth flow control.

In modulating applications, a built-in positioner continuously compares the command signal received from the PLC or higher-level controller with the actual stem position measured by the feedback sensor. It automatically corrects any deviation until the error is eliminated, ensuring continuous real-time valve positioning with high precision.

What Is the Purpose of a Linear Electric Actuator?

The primary purpose of a linear actuator is the automation of control valves in industrial processes. Its role goes far beyond simply opening and closing a valve. Instead, it continuously maintains critical process parameters such as temperature, pressure, flow rate, and liquid level. A control valve electric actuator performs four essential functions:

1. Precise Valve Positioning

The actuator positions the valve stem anywhere within its full stroke with an accuracy of approximately 1%, while premium models can achieve positioning accuracy of up to 0.1%. This level of precision is critical because valve position directly affects process quality, including steam temperature at a boiler outlet, chemical dosing accuracy, or pressure regulation within industrial systems.

2. Smooth Motion Control

The actuator moves the stem without sudden impacts, using programmable acceleration and deceleration at the beginning and end of each stroke. This minimizes water hammer, extends valve service life, and improves control stability. Smooth operation is particularly important in industries such as chemical processing, pharmaceuticals, district heating, and other applications sensitive to rapid flow changes.

3. Flow Regulation

By adjusting the stem travel, the actuator changes the valve opening and therefore controls the flow rate of liquids or gases. In control loops, it maintains the required flow regardless of fluctuations in system pressure or temperature.

4. Integration with Industrial Automation Systems

Electric actuators operate as final control elements within industrial automation systems. They receive commands from PLCs or SCADA systems through analog signals (4–20 mA) or digital communication protocols such as Modbus RTU/TCP, Profibus DP, or HART. At the same time, they transmit diagnostic data including valve position, output thrust, temperature, and cycle count, enabling real-time monitoring of every control valve in the system.

Types of Linear Electric Actuators

Linear actuators are classified according to four primary criteria, each affecting equipment selection for a specific application.

By Application

• Modulating Actuators – equipped with an integrated positioner and designed for continuous valve positioning using a 4–20 mA control signal.
• On/Off & Modulating Actuators – capable of both open/close operation and continuous modulation, with operating mode selected through software configuration.
• On/Off Actuators – simplified models intended only for fully opening or fully closing valves.

By Output Thrust

Available from compact models delivering 0.5–2 kN for HVAC and small process valves to heavy-duty actuators producing 50–200 kN or more for large-diameter control valves in the oil & gas, petrochemical, and power industries.

By Power Supply

Three-phase 380 V for most industrial installations, single-phase 230 V for compact process equipment, and 24 V DC versions for applications requiring emergency battery backup.

By Construction

• Industrial Standard – designed for conventional industrial environments.
• Explosion-Proof – Ex d, Ex de, and Ex e versions certified according to ATEX and IECEx standards for hazardous areas in oil & gas and petrochemical facilities.
• Corrosion-Resistant – manufactured using corrosion-resistant materials and protective coatings for aggressive environments.
• High-Temperature Version – intended for installation near steam lines and high-temperature process piping.

Key Specifications

When selecting a control valve electric actuator, seven technical parameters are particularly important:

Additional selection criteria include the type of position feedback (potentiometer, encoder, or digital position sensor), availability of manual override using a handwheel, and the type of limit and torque switches.

Applications

Electric actuators for control valves are a fundamental component of automation in any process requiring continuous control of flow or pressure. Their primary industrial applications include:

• Thermal Power Generation and District Heating. Control valves in CHP plants, boiler houses, and district heating substations are used to maintain steam temperature, pressure, and heat transfer fluid flow. This is one of the most common applications for linear actuators.
• Oil & Gas Industry. Pressure and flow control at throttling stations, pressure reduction units, gas distribution stations, and oil & gas processing facilities. Most actuators in this sector are supplied in explosion-proof ATEX/IECEx-certified versions.
• Petrochemical and Chemical Industries. Dosing systems, chemical injection lines, and process control involving aggressive media. Smooth motion control, water hammer protection, precise positioning, and corrosion-resistant construction are essential requirements in these environments.
• Power Generation and Nuclear Facilities. Control valves used in auxiliary circuits, cooling water systems, and steam pipelines. These applications require maximum reliability, industry certifications, and service life measured in tens of thousands of operating cycles.

Buy a Linear Electric Actuator

Our product range includes electric actuators from the Austrian manufacturer Schiebel, one of Europe’s leading suppliers of actuator solutions for the oil & gas industry, power generation, and nuclear facilities.

When you order from us, you receive:

• Professional actuator selection based on your specific control valve and process requirements, including output thrust, stem stroke, travel speed, and communication protocol.
• Official supply with a complete package of technical documentation.
• Engineering support before and after purchase, including assistance with positioner configuration, PLC/SCADA integration, and communication protocol setup.
• Manufacturer’s warranty according to the equipment documentation.
• Fast delivery.

The price of a linear electric actuator depends on the required output thrust, industrial or explosion-proof execution, control type (with or without an integrated positioner), and available communication interfaces. We will prepare an accurate quotation after reviewing the specifications of your control valve and application requirements.

FAQ

How do I determine the required output thrust?

Use the valve stem operating force specified by the valve manufacturer and add a safety margin of approximately 25–30%. This compensates for increased differential pressure, stem friction over time, and thermal expansion during operation. For example, if the required operating force is 8 kN, an actuator rated at approximately 10–10.5 kN is recommended. Selecting an actuator without sufficient safety margin may prevent the valve from closing under abnormal operating conditions.

How do I choose the correct stem stroke?

The actuator stroke must match the full travel specified for the control valve. If the valve requires a 40 mm stroke, the actuator should provide at least 40 mm of travel, preferably with an additional safety margin of 5–10 mm. Insufficient stroke prevents the valve from fully opening, while excessive stroke may cause mechanical impacts at the end positions and accelerate component wear. Custom stroke lengths can be supplied when standard models are not suitable.

What is the expected service life?

European industrial linear actuators are typically designed for 10,000–25,000 full open/close cycles or between 1 and 5 million short positioning movements in continuous modulating applications. Under normal operating conditions, this corresponds to an expected service life of approximately 12–20 years. Actual lifetime depends on operating frequency, temperature, humidity, vibration, and regular maintenance, including gearbox lubrication and inspection of torque switches.

Do linear actuators support the Modbus protocol?

Yes. Modern microprocessor-controlled actuators support Modbus RTU (RS-485), Modbus TCP (Ethernet), as well as Profibus DP and HART communication. These protocols allow both control commands and diagnostic information to be exchanged, including valve position, output thrust, motor temperature, operating cycle count, and fault history, providing complete real-time monitoring through SCADA systems.

Can a linear actuator be used in hazardous areas?

Yes. Explosion-proof linear electric actuators are available in Ex d, Ex de, and Ex e versions with ATEX and IECEx certification for operation in hazardous gas Zones 1 and 2, as well as dust Zones 21 and 22. These actuators are widely used on oil & gas facilities, gas distribution stations, petrochemical plants, and other hazardous industrial installations.

What is the difference between a linear actuator and a multi-turn actuator?

The main difference is the type of motion and intended application. A linear actuator produces straight-line movement of the valve stem and is primarily used with control valves requiring accurate positioning and smooth modulation. A multi-turn actuator rotates a threaded stem through multiple revolutions and is typically used with gate valves, globe valves, and other rising-stem valves where high torque and long travel are required. Although both types can be configured for on/off or modulating service, linear actuators remain the standard solution for continuous process flow control.

Need Help Selecting an Electric Actuator for Your Control Valve?

Contact our engineering team or submit an inquiry through our website. We will review your valve specifications—including required output thrust, stem stroke, and control signal—and prepare a detailed technical proposal together with a commercial quotation.