Hydraulic actuator (self-contained electro-hydraulic actuator that moves process valves and dampers)
Self-contained electro-hydraulic actuators for valves and dampers · an electric motor and pump in the actuator instead of a hydraulic plant, spring or accumulator fail-safe, ESD modes, duty rating, positioning accuracy and design life, and where steel plants use them
A self-contained electro-hydraulic actuator puts the hydraulic power unit inside the actuator: an electric motor drives a small pump, solenoid valves direct oil to a cylinder, and a spring or accumulator drives the valve to its safe position when power or the shutdown signal is lost. It is chosen where a valve or damper needs high force, fine positioning or a guaranteed fail-safe stroke without a plant air or hydraulic supply. Specify the force, the fail action and what triggers it, the duty, and the positioning performance.
Self-contained electro-hydraulic (electraulic) actuators for quarter-turn and linear valves, gates and dampers, with spring or accumulator fail-safe, ESD and positioning control. Pneumatic quarter-turn actuators are covered on the Pneumatic actuator page; electric actuators in flow loops on the Liquid flow controller with electric valve actuator page; mounting interfaces on the Valve actuator mounting page; limit switch boxes on the Valve position indicator and limit switch box page; separate hydraulic power units on the Hydraulic power unit page; servo cylinders for mould oscillation on the Servo actuator unit for continuous casting mould oscillation page.
CNFX editorial research · Sources checked October 12, 2026 · 3 sources
Rotork describes its Skilmatic SI actuators as combining "the simplicity of electrical operation with the precision of hydraulic control and the reliability of mechanical spring-return fail-safe action", with quarter-turn torque "from 75 to 200,000 Nm" and linear thrust "up to 400 kN". Its motors are integral and "started under no load"; a hand pump and lockable selector valve form the optional manual override. [1] REXA calls its XPAC Series 3 an "Electraulic™ Actuator" with a motor and pump system, closed-loop hydraulics, "No Routine Fluid Maintenance" and "100% Duty Cycle Motors". [2]
Rotork's SI can be configured to fail safe in three ways, "loss of ESD signal and/or power supply, loss of ESD signal only and loss of power supply only", is certified to IEC 61508:2010 for Safety Instrumented Systems, or can stay put on loss of power for non-fail-safe duties. For a temporary loss of ESD signal or power before the safe position is reached, it can be set to stop and wait, return to the previous position, continue to the safe position, or continue and wait for a manual reset. [1]
On SI4 actuators, "Accumulators can be sized to give multiple strokes of operation on loss of power supply or control signal." [1] REXA lists spring or accumulator fail-safe and redundant construction as options. [2]
State the safe position, which losses must trigger it (power, ESD signal, both), the stroke time required in each direction, whether a SIL rating is needed, and how many strokes must be available without power.
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Duty, positioning accuracy and design life
Rotork rates SI3-SR and SI4-SR on-off and positioning duty at "< 15 cycles/hour" and modulating duty at 300 starts per hour at 75% rated duty below 40 °C, falling to 40% above 40 °C. With a 4-20 mA signal, accuracy runs from 1% (resolution 3%) on its smallest RH-030 and sub-48 kN linear sizes to 0.25% (0.5%) on the largest; minimum design life runs from 60,000 cycles on RH sizes to 2,500 cycles on GH-350 and sub-500 kN linear actuators. [1]
REXA lists metals-plant duties for its actuators including blast furnace gas pressure control, hot blast temperature control, coke oven crossover valve pressure, reheat furnace pressure and baghouse gas pressure. [3]
Give the control mode (on-off, positioning, modulating), expected starts per hour and ambient temperature, so the rating can be checked against the actuator's duty classification.
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Electro-hydraulic actuator details
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3 companies list this product among what they make. Company figures are quoted from each
company's own website; every card states where the relationship came from.
Zhejiang Bigtork Valve Automation Co., Ltd.
Manufacturing site to be confirmed for the order
Lists hydraulic actuators and hydraulic linear actuators alongside scotch yoke and rack-and-pinion pneumatic valve actuators.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why choose electro-hydraulic over pneumatic?
It needs only electric power yet gives hydraulic force and a spring or accumulator fail-safe; Rotork's SI reaches 200,000 Nm quarter-turn. [1]
What happens on loss of power?
Depending on configuration, Rotork's SI fails safe on loss of power and/or ESD signal, or stays put for non-fail-safe duties. [1]
Can it modulate continuously?
REXA states 100% duty cycle motors; Rotork rates modulating duty at 300 starts per hour at 75% rated duty below 40 °C. [2][1]
Where are they used in steel plants?
REXA lists blast furnace gas pressure, hot blast temperature, coke oven and reheat furnace pressure control among its metals applications. [3]
Sources and what still needs a direct check
Sources checked 2026-10-12. Rotork publishes the Skilmatic SI range datasheet; REXA publishes its XPAC Series 3 product page and metals processing applications.
