What is an electro-hydraulic actuator?

A self-contained actuator with an electric motor-driven hydraulic pump built in: power and a signal in, high-thrust hydraulic motion out. No external hydraulic power unit or instrument air needed.

Why choose electro-hydraulic over pure electric?

Thrust density. Oil at hundreds of bar delivers forces a motor-gearbox would need an enormous frame for — while still only requiring a power cable and signal pair at the valve.

How does it fail safe on power loss?

By stored energy: mechanical springs drive the fail stroke (the certified, mechanically certain option), or a charged accumulator completes the stroke through the valving.

Where is electro-hydraulic the standard choice?

HIPPS and high-integrity ESD isolation, offshore platforms without instrument air, large chokes and gates on remote pads, and subsea packages.

What maintenance does it need?

The same fluid-power discipline as any hydraulic system — oil level and cleanliness, seal integrity, strainer service — plus scheduled proof tests of the fail path.

Electro-Hydraulic Actuators

Actuator hub Self-contained fluid power per actuator practice

Electro-hydraulic valve actuator — **Reading the hardware.** An electro-hydraulic actuator: an electric motor-driven pump and hydraulic circuit packed inside the actuator housing. Power in, extreme thrust out — with springs or accumulators standing by for the fail stroke.

An electro-hydraulic actuator (EHD) builds the hydraulic power unit into the actuator itself: an electric pump charges a compact hydraulic circuit, and oil pressure drives the piston with the force density only oil provides. You get electric-actuator simplicity of supply (just power and a signal) with hydraulic-actuator thrust — and, in spring or accumulator builds, a genuine fail stroke on power loss.

How It Works

A motor-driven pump pressurises the internal circuit against an accumulator; directional valving ports oil to the actuating piston. On power loss, stored energy does the failing:

Spring-return — mechanical springs drive the fail stroke (the certified choice)
Accumulator reserve — pressurised nitrogen completes the stroke electrically-valved
Pump sizing — sets stroking speed; large thrust + fast stroke = serious pump duty
Directional control — solenoid or pilot valves route oil per command
Modulating builds — servo/proportional valving tracks a positioner-style command
Subsea variants — compensated housings and ROV hotstab interfaces

Types & Variants

Linear EHD — gate/globe isolation and HIPPS thrust
Quarter-turn EHD — yoke kinematics on an internal power pack
HIPPS / SIS certified — fail-safe data for proof testing
Modulating EHD — proportional valving for throttling duty
Explosion-proof — Exd motors and housings for process zones
Subsea EHD — depth-rated, pressure-compensated builds

What to Compare Before You Buy

Parameter	What it means	Why it matters
Thrust / torque & stroke time	Seat load vs pump flow at minimum voltage	Pump flow, not just pressure, sets stroking speed — HIPPS strokes are contractual
Fail-safe mechanism	Spring vs accumulator reserve	Springs are mechanically certain; accumulators depend on valving and charge
Duty & thermal rating	Pump starts per hour, modulating capability	Frequent stroking heats the pump motor; verify the duty cycle
Power supply quality	Voltage sag, backup power availability	The pump is an electric machine — size against minimum voltage
Certification	SIL data, Exd, subsea depth rating	Match the safety study and area classification paperwork
Maintenance model	Oil condition, seals, onboard diagnostics	Self-contained units need scheduled oil and seal service like any HPU

Where It Is Used

High-thrust duty where compressed air does not exist and electric thrust alone would be enormous:

HIPPS and high-integrity ESD isolation (certified fail stroke)
Offshore platforms without instrument air at the valve location
Large choke and gate valves on remote pads
Subsea and harsh-environment actuation packages

Common Brands

Biffi (Baker Hughes) Biffi (Baker Hughes) — EH series electro-hydraulic actuators; HIPPS packages. Rotork Rotork — Fluid-power portfolio including self-contained EHD builds. Full profile → Emerson (Bettis) Emerson (Bettis) — Electro-hydraulic variants of the Bettis actuator line. Flowserve Flowserve — EHD actuation matched to severe-service valve lines. Bernard Controls Bernard Controls — Electro-hydraulic packages for high-thrust linear duty. Severn Glocon Severn Glocon — Engineered electro-hydraulic actuation for severe service. Full profile →

Field Problems & Fixes

Symptom	Likely cause	Fix
Stroke time got slower	Pump wear, clogged suction strainer, low oil level	Service pump and strainer; verify oil level and cleanliness
Fail stroke did not complete	Accumulator lost charge or valve stuck; spring pack degraded	Proof-test the fail path; recharge/replace accumulator or springs
Motor thermal trips	Duty exceeded pump-motor rating	Re-rate the duty cycle; upsize the unit
Position hunting in modulating service	Proportional valve contamination or tuning	Filter the oil; retune the servo loop
Internal leakage / creep	Cylinder seal wear or directional valve bypass	Seal kits; test and service the valving

Related: Hydraulic actuators (HPU-fed), gas-over-oil actuators and all accessories.

Note. Generic engineering description for education. Brand names above are trademarks of their respective owners; RegValve.com is not affiliated with or endorsed by them. For installation and safety settings, follow the manufacturer’s manual and your plant procedures.