Linear Electric Actuator for Globe and Single-Seat Control Valves

Globe and single-seat control valves do not rotate; their stems move straight down onto the seat. This linear electric actuator delivers 1–50 kN of thrust over strokes up to 100 mm, driving the plug precisely against flow and pressure forces with no instrument air required. With an optional 4–20 mA positioner it becomes a complete electric final control element for boiler, process and skid-mounted control valves.

Why Do You Need a Linear Electric Actuator?

Most control valves in your plant are probably pneumatically actuated, which means they depend on a continuous supply of clean, dry instrument air. Where that air is unavailable, unreliable or expensive to install — remote skids, small plants, winter-cold sites, offshore topsides — an electric linear actuator removes the whole air chain: compressor, dryer, filter, regulator, tubing and I/P converter. It also solves a mechanical problem: seating a globe valve against high process pressure requires real thrust, delivered in a straight line, and a rotary actuator cannot provide it without a linkage that adds backlash and wear.

Electric linear actuation changes the maintenance story too. There is no diaphragm to rupture, no air filter to service, no leaking fittings, and no positioner calibration drift caused by supply-pressure variation. The table below compares four operating conditions where pneumatic or manual linear operation typically creates cost or risk.

Working Principle: Turning Torque into Straight-Line Thrust

Inside the actuator, a motor drives a high-efficiency ball screw or roller screw through a reduction gear. The screw converts rotary motion into linear motion of the output stem, which connects through a coupling to the valve stem. Because the screw is self-locking in the standard configuration, the valve plug holds its position whenever the motor stops, without the constant air pressure that a pneumatic diaphragm needs to stay put.

Two measured quantities protect the valve: stroke and thrust. A travel sensor tracks the stem position for precise open/close and modulating control, while a thrust sensing system continuously measures the force applied to the stem. If the plug meets an obstruction, seat wear increases resistance, or the valve is commanded beyond its mechanical travel, the thrust limit cuts motor power before the stem or seat is damaged. On modulating versions, a built-in positioner compares the 4–20 mA setpoint with the measured stem position and drives the motor until the error is zero, giving the control loop a stable, repeatable final element.

Structural Advantages Built for Control-Valve Service

• Ball screw drive: high mechanical efficiency means a smaller motor for the same thrust, less heat and longer service life.
• Adjustable thrust protection: the thrust limit is set to match your valve seat load, preventing over-tightening and stem damage.
• Integrated positioner option: 4–20 mA setpoint input, position feedback and local manual controls in one housing.
• Self-locking drive: holds stem position with power off, eliminating drift and brake wear.
• Rugged sealed housing: IP65 standard, IP67 option, with anti-condensation heater for humid and cold sites.

Selection Guide: Sizing Thrust and Stroke for Linear Valves

Two numbers define the selection. The required thrust equals the unbalanced force from the process pressure acting on the plug area, plus packing friction, plus the seat load needed for tight shutoff; add a safety margin of 25–30% for dynamic effects. The required stroke is the valve manufacturer's rated travel from closed to full open, typically 25 to 100 mm for globe valves. Then confirm the mounting arrangement: yoke-mounted actuators connect directly to the valve bonnet, while bracket-mounted units suit valves with their own yokes. The table below gives typical guidance; final sizing should use the valve data sheet.

Typical Applications

This linear actuator is applied wherever a globe-type control valve must move straight, precisely and without air utilities.

Key Product Advantages

• 1–50 kN thrust range: sized for globe, single-seat and cage valves from DN25 to DN200.
• No instrument air required: eliminates compressors, dryers, tubing and freeze risk, cutting both capex and opex.
• 4–20 mA modulating option: built-in positioner with ±1% accuracy for closed-loop control.
• Adjustable thrust limit: protects valve seat and stem while guaranteeing tight shutoff at the set force.
• Ball screw efficiency: lower power consumption and heat generation than worm-driven linear units.
• Self-locking stem: valve position is held with power off, with no diaphragm bleed or brake wear.
• Stroke and speed flexibility: 25–100 mm strokes and selectable traverse speeds match valve travel time requirements.
• 100% factory thrust-tested: each unit is calibrated and load-tested before shipment, with the certificate supplied.

Technical Specifications

Frequently Asked Questions

1. How do I calculate the thrust required for my control valve?

Add three components: the unbalanced force created by the process pressure acting on the plug area, the packing friction of the valve stem, and the seat load needed for the required shutoff class. Multiply the total by a safety factor of 1.25 to 1.3 for dynamic effects and future packing adjustment. The valve data sheet normally lists the required actuator thrust; if it does not, send us the valve type, size, pressure rating, trim style and process conditions, and our engineers will calculate the thrust class. Undersized thrust shows up as incomplete shutoff or a valve that stalls near the seat, so it is worth confirming before ordering.

2. Can this actuator replace my existing pneumatic diaphragm actuator?

In most cases, yes. The actuator must provide at least the same thrust and stroke as the pneumatic unit, and the mounting must match the valve bonnet or existing yoke. Because electric actuators are self-contained, the conversion removes the air supply line, positioner, I/P converter and related maintenance from that loop. The 4–20 mA setpoint wiring is identical to what the positioner already receives, so the DCS configuration is unchanged. Before conversion, verify fail-safe requirements: a pneumatic spring-to-close valve gives fail-safe action on air loss, so if your process needs automatic fail-safe positioning, discuss the electric fail-safe options with our engineers.

3. What is the difference between the on/off and modulating versions?

The on/off version drives the stem to the fully open or fully closed position using limit switches, and is intended for isolation duty. The modulating version includes a built-in positioner that compares a 4–20 mA or 0–10 V setpoint with the measured stem position and moves the valve to any intermediate point, holding it there against process forces. The modulating version also has a duty-rated motor for frequent reversals, which is essential in throttling service. If a process valve must hold positions such as 40% or 65% open, choose the modulating version; using an on/off unit for throttling overheats the motor and produces poor control.

4. How is the stroke set during commissioning?

Stroke setting is done in manual mode using the local controls. First, drive the stem to the mechanical fully closed position against the valve seat at low speed, then record that as the zero point. Next, drive to the fully open position defined by the valve manufacturer's rated travel and record the upper limit. The actuator stores both positions, and the modulating version maps the 4–20 mA range across the measured stroke automatically. Re-zeroing is recommended after valve maintenance that changes the stem connection. The procedure takes a few minutes and is described step by step in the manual, with remote support available from our engineers.

5. How fast will the valve travel, and can the speed be changed?

Traverse speed depends on the model and is selected to match the process requirement: typical speeds range from 8 to 40 mm per minute. Slow speeds suit level and temperature loops where abrupt movement would disturb the process; higher speeds suit isolation and bypass duties where response time matters. If the valve must stroke from fully closed to fully open in a defined time, tell us the stroke and the required time when ordering, and we will select the correct gear ratio. Unlike pneumatic actuators, the speed does not depend on air supply pressure, so behavior is identical in summer and winter.

6. What maintenance does a linear electric actuator require?

Very little compared with pneumatic systems. There is no air filter to change, no diaphragm to inspect and no I/P converter to recalibrate. The recommended schedule is a six-monthly external check of cable glands, mounting bolts and the stem coupling, and an annual verification that the reported position matches the actual stem position and that the thrust limit still trips at the set value. The ball screw is factory lubricated; re-lubrication intervals are stated in the manual and depend on stroke frequency. In clean indoor service, these actuators typically run for years between interventions, and the diagnostics history helps you schedule service before problems appear.

Why Choose Our Electric Actuator?

QINWEIYB designs and builds linear electric actuators for control-valve duty in our ISO 9001 certified factory, where every unit is thrust-calibrated and stroke-tested before dispatch. You receive the calibration certificate, installation drawing and manual with each actuator, and direct access to our application engineers for sizing, conversion advice and commissioning support. Because we manufacture rather than trade, spare parts and technical answers come from the people who designed the product, and your project gets a single accountable partner from quotation to start-up.