Cematic Electric Linear Actuators — Precise Linear Movement for Globe, Gate Valves, and Control Devices

The electric linear actuator is the correct type of actuator when the valve to be automated does not operate by rotational turning but by axial stem displacement: globe valves with a disc plug on a conical seat, non-rising stem gate valves, linear diaphragm valves, pressure regulators, and any other control device that requires a controlled push or pull force to modify its position. Where the quarter-turn actuator converts its energy into rotation, the linear actuator converts it into linear force — thrust measured in kilograms-force (kgf) or pounds-force (lbf) applied directly to the valve stem.

Cematic linear actuators are available in two configurations depending on the installation environment: the standard version (non-classified area, IP67 protection) and the Ex-proof version with ATEX, IECEx, and CSA certification for installations in Zone 1 and Zone 2 with the presence of flammable gases or dusts. Both configurations share the same operating principle and the same control and communication capabilities, with the difference being in the design and certification of the enclosure.

When is a linear actuator needed instead of a quarter-turn one?

The first question when specifying an actuator is always the type of valve movement:

• Globe valve: Its obturating disc moves perpendicular to the flow axis — it opens and closes by vertical linear displacement of the stem. Requires a linear actuator. It is the most commonly used control valve in industrial processes due to its linear or equal percentage flow characteristic and its precise regulation capability.
• Non-rising stem (NRS) gate valve: The wedge moves linearly without rotating. Requires a linear actuator. The quarter-turn actuator cannot operate it because there is no direct connection interface to the rotating stem.
• Linear diaphragm valve: The diaphragm is compressed or released by the displacement of the actuator stem. Requires a linear actuator.
• Pressure regulators and process control valves: Most conventional process control valves have linear stem movement with a stroke of 25 to 100 mm.
• Ball or butterfly valve: 90° rotational movement → Requires a quarter-turn actuator, not linear.

Operating principle of the Cematic electric linear actuator

The Cematic linear actuator converts the rotational movement of the electric motor into linear displacement using a lead screw or trapezoidal screw mechanism integrated into the housing. The operating cycle is as follows:

1. Signal reception: The DCS or PLC's PID controller sends the setpoint signal — analog 4–20 mA for modulating control, or digital signal for full open/close.
2. DC motor actuation: The DC motor with 75% duty cycle rotates in the direction corresponding to the required movement (stem extension or retraction).
3. Rotation → translation conversion: The internal transmission converts the motor's rotation into linear displacement of the output stem at a constant speed of 0.46 mm/second.
4. Proportional positioning: The modulating control unit compares the actual stem position (measured by the internal potentiometer) with the received setpoint and adjusts the motor's movement until the actual position matches the setpoint.
5. Feedback to the control system: The analog output signal (4–20 mA or 2–10 V) confirms the actual stem position to the controller in real-time, closing the control loop.
6. Overload protection: Integrated force switches detect when the thrust force exceeds the actuator's nominal value — due to a mechanical obstruction, a clogged seat, or a stuck valve — and automatically cut off the motor, protecting both the actuator and the valve's internal components.

Technical characteristics of Cematic linear actuators

• Type of movement: Linear — extension and retraction of the output stem
• Linear speed: 0.46 mm/sec (0.018 in/sec) constant across all models
• Motor: DC with 75% duty cycle — the highest duty cycle in the Cematic range, suitable for control loops with frequent position adjustments
• Modulating control: Factory included as standard on all models. Accepted analog inputs: 4–20 mA, 1–5 V, 2–10 V. Position feedback output: 4–20 mA and 2–10 V.
• Force overload protection: 2 integrated force switches that cut off the motor in case of over-torque — standard protection on all models
• Adjustable stroke: The length of the stem's travel can be adjusted in the field to adapt to the specific stroke of the valve to be operated — no specific model required for each stroke length
• Valve interface: ISO 5210 — the international standard for the mounting interface between linear actuators and process valves. Ensures direct compatibility with globe and gate valves from all manufacturers that comply with the standard.
• Manual override: Manual operating handwheel integrated into all models for emergency operation without electrical supply. The handwheel allows manual stem movement in case of power failure without dismounting the actuator from the valve.
• Gears: High-alloy steel with self-locking system that prevents position rollback due to vibration, differential pressure variation, or changes in valve load
• Motor insulation: Class F
• Standard IP protection: IP67 — dust-tight and temporary immersion up to 1 meter
• IP protection for Ex-proof version: IP68 — 7 meters for 72 hours
• Operating temperature: -30 °C to +70 °C standard; -30 °C to +65 °C for CSA version for North America
• Working relative humidity: 30% to 95%
• Housing: Die-cast aluminum with epoxy polyester paint

Available models — force, weight, and maximum stroke

Displacement speed based on 110 VAC / 60 Hz / 75% duty cycle.

Available power supply voltages

• 24 VDC: For powering from modern PLCs, regulated power supplies, and automation systems with standard DC power. Compatible with Allen-Bradley, Siemens, Mitsubishi, and Schneider control panels.
• 24 VAC: For building management systems (BMS) and HVAC that use 24 VAC transformers as a standard control source.
• 110–120 VAC / 60 Hz: The most frequent mains voltage in industrial installations in Mexico. No need for additional transformer to power from standard control panels.
• 220–240 VAC / 50–60 Hz: For installations with two-phase supply or where distance to the panel causes unacceptable voltage drop at 110 VAC.

ISO 5210 Interface — compatibility with valves from all manufacturers

The ISO 5210 standard is the linear equivalent of the rotary ISO 5211: it defines the mounting plate dimensions and the connection to the valve stem for linear motion actuators. This standardization ensures that the Cematic linear actuator mounts directly on globe and gate valves from any manufacturer that complies with the standard, without adapters or field machining. The two available interfaces are:

• ISO 5210 F07: For LE-250 and LE-500 models — globe valves DN25 to DN80 (1" to 3") and small to medium diameter gate valves
• ISO 5210 F10: For LE-1000 and LE-2000 models — globe valves DN100 to DN200 (4" to 8") and medium to large diameter gate valves

Modulating control — why it's standard and not optional

The decision to include factory modulating control in all models reflects the reality of linear actuator use: unlike the quarter-turn actuator — which in many applications only needs ON/OFF — the linear actuator is mostly installed on globe valves that are the control element of a PID loop. In this context, modulating control is not an optional accessory but the main function of the actuator. The control signal data are:

• Input signal (controller setpoint): 4–20 mA / 1–5 V / 2–10 V — selectable according to the analog output type of the PID controller or DCS
• Feedback signal (actual position to controller): 4–20 mA and 2–10 V — the controller receives continuous confirmation of the actual stem position to close the control loop
• Positioning accuracy: ±1–2% of the full stroke range
• Resolution: Determined by the speed of 0.46 mm/sec and the response time of the internal modulating controller

Explosion-Proof (Ex-proof) Version — ATEX, IECEx, and CSA

For installations in classified areas such as Zone 1 or Zone 2 (flammable gases) and Zone 21 or Zone 22 (combustible dusts), Cematic linear actuators are available in an explosion-proof version with the following certifications:

• ATEX II 2 GD: Ex db IIB T4 Gb / Ex tb IIIC T130°C Db — for the European Union (standards EN IEC 60079-0, EN 60079-1, EN 60079-31)
• IECEx: Ex db IIB T4 Gb / Ex tb IIIC T130°C Db — international recognition in over 50 countries
• CSA — Zones System: Class I Zone 1 Groups IIA/IIB T4 / Class II Zone 21 Groups IIIA/IIIB/IIIC T130°C — for projects with North American requirements

The Ex-proof version raises the IP protection to IP68 (7 meters / 72 hours) and has an operating temperature of -30 °C to +65 °C for the CSA version. Modbus RTU RS-485 communication is available as an option in the Ex-proof version. For complete information on the Ex-proof version, consult the Cematic explosion-proof actuators category.

Available options and accessories

• Anti-condensation heating resistor: Raises the internal temperature to prevent lubricant freezing and keep the interior dry in environments with high temperature variation. Not recommended if ambient temperature continuously exceeds 35 °C. Recommended in combination with the heater thermostat.
• Heater thermostat: Disconnects the resistor when the internal temperature exceeds 25 ±5 °C — optimizes the electrical consumption of the heating.
• Modbus RTU RS-485 communication: Available in the Ex-proof version. Allows direct integration with SCADA and DCS systems without additional analog signals. Up to 32 actuators in a daisy chain over a single pair of RS-485 cables.
• Optional conduit entries: Standard 2 × ½" NPT. Options: 2 × ¾" NPT, 2 × M20, 2 × M25 — for compatibility with existing conduit systems in the installation.

Sizing guide — how to select the correct model

Selecting the correct linear actuator requires knowing three parameters of the process and the valve:

1. Required operating force (Thrust)

The operating force required to move the stem depends on the valve type, diameter, working differential pressure, and seat type. As a general reference:

• Globe valves DN25–DN50 (1"–2") at pressures up to 10 bar: 250–500 kgf → LE-250 or LE-500
• Globe valves DN65–DN100 (2½"–4") at pressures up to 16 bar: 500–1,000 kgf → LE-500 or LE-1000
• Globe valves DN125–DN200 (5"–8") or high differential pressure: 1,000–2,000 kgf → LE-1000 or LE-2000

Always apply a minimum safety factor of 1.25 over the valve's maximum operating force. The valve manufacturer provides the required force curve as a function of stem position and differential pressure — request it before specifying the actuator.

2. Valve Stroke

Stroke is the total displacement of the stem from fully closed to fully open position. LE-250 and LE-500 models have a maximum stroke of 50 mm (2 inches) — sufficient for globe valves up to DN100 in most standard designs. LE-1000 and LE-2000 models have a maximum stroke of 100 mm (4 inches) for larger diameter valves or designs with longer stem travel. The stroke is adjustable in the field within the maximum range of the selected model.

3. Available voltage at the installation point

Verify the actual voltage of the control panel or the nearest power supply point: 24 VDC, 24 VAC, 110 VAC, or 220 VAC. An actuator specified with incorrect voltage can result in irreversible motor damage.

Don't have your valve's force data? Share the manufacturer, model, diameter, and working pressure with us, and our technical team will calculate the required force and recommend the correct model at no additional cost.

Linear actuator vs. pneumatic actuator — when to choose electric?

Choose electric linear actuator when: No compressed air network is available, digital integration with the DCS or PLC is a priority, adjustment frequency is moderate (temperature control loops with long time constants), or the installation is in a remote area without pneumatic infrastructure.

Choose pneumatic linear actuator when: A compressed air network already exists, response speed is critical (pressure or flow control loops with short time constants), or spring fail-safe is required without relying on electrical components.

Main industries and applications

• Power generation — steam plants: Control of globe valves in process steam lines: regulation of heating steam temperature in heat exchangers, boiler feedwater flow control, and process turbine steam regulation. The electric linear actuator is the alternative when the plant does not have an instrumentation air system available at the control point.
• Chemical and petrochemical industry: Control of globe valves in reactor temperature loops, regulation of reactant flow in distillation columns, and pressure control in condensation systems. The Ex-proof version for Zone 1 installations in petrochemical plants. See also Cematic Ex-proof actuators.
• Industrial and building HVAC: Globe control valves in industrial building, hospital, and data center heating steam systems. The integrated 4–20 mA modulating control allows direct integration with zone temperature controllers (BMS/BACnet via protocol converter).
• Food and pharmaceutical industry: Temperature control in pasteurizers, sterilizers, and process heat exchangers. The controlled speed of the linear actuator (0.46 mm/sec) is appropriate for these temperature loops where time constants are long and high response speed is not required.
• Water treatment — potable water plants: Control of globe valves in pressure filtration systems, flow regulation in pressure sand filters, and valve control in softening and reverse osmosis systems.
• Industrial cogeneration: Control of process steam in cogeneration plants where the control system is electric and no pneumatic infrastructure is available for steam valve actuators.
• General manufacturing — steam heating systems: Temperature control in rubber curing presses, vulcanizers, autoclaves, and heat treatment equipment where the steam globe valve requires proportional control from a PID temperature controller.

Why choose Cematic linear actuators?

The Cematic range of linear actuators combines verified technical specifications — real force in kgf, constant speed of 0.46 mm/sec, adjustable stroke, standard modulating control — with stock availability in Mexico City and technical support for correct sizing. We calculate the required force using your valve data, verify the necessary stroke, and confirm the correct voltage for your control system. For projects in classified areas, we offer the Ex-proof version with ATEX, IECEx, and CSA certification with complete technical documentation. Technical quotation on the same business day. Shipments throughout the Mexican Republic. Contact us via WhatsApp or at ventas@cematic.com.