Hydraulic Actuators: How They Work, Types & Applications
Learn what a hydraulic actuator is, how it converts hydraulic energy into movement, and the difference between linear and rotary hydraulic actuation.
Last Updated: 25 August 2026
A hydraulic actuator is a device that converts hydraulic energy into mechanical motion.
Pressurised hydraulic fluid acts on internal components such as a piston, vane or rotating element, creating either linear movement or rotary movement.
Hydraulic actuators are used across industrial machinery, construction equipment, mobile plant, marine systems, manufacturing equipment and many other applications where controlled force or movement is required.
In many hydraulic systems, the actuator is the component that actually performs the work.
For a wider overview of hydraulic system operation, see our hydraulic systems guide.
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Check Your Oil NowQuick Answer: What Is a Hydraulic Actuator?
A hydraulic actuator converts the energy carried by pressurised hydraulic fluid into useful mechanical movement.
The movement may be linear, as with a hydraulic cylinder, or rotary, as with a hydraulic motor or rotary actuator.
The actuator is therefore the part of the hydraulic system that turns hydraulic pressure and flow into force, torque and physical motion.
What Does a Hydraulic Actuator Do in a Hydraulic System?
A hydraulic system transfers energy through pressurised fluid.
The pump creates hydraulic flow.
Valves control where that flow goes and how the system behaves.
The actuator then converts that hydraulic energy into movement.
A simplified hydraulic power path looks like this:
01 — PUMP
The hydraulic pump creates fluid flow within the system.
02 — CONTROL
Valves direct and regulate the hydraulic fluid.
03 — ACTUATE
Pressurised fluid reaches the hydraulic actuator.
04 — MOVE
The actuator converts hydraulic energy into linear force or rotary torque.
How Does a Hydraulic Actuator Work?
A hydraulic actuator works by using pressurised fluid to create force against an internal area.
In a hydraulic cylinder, for example, pressurised oil enters the cylinder and acts on the piston.
The pressure acting across the effective piston area creates force. That force causes the piston and piston rod to move, producing linear motion.
In a double-acting cylinder, hydraulic fluid can be directed to opposite sides of the piston so that hydraulic power controls both extension and retraction.
Engineering Principle
Hydraulic pressure creates force by acting over an area. The force available from a cylinder therefore depends on factors including system pressure and the effective piston area.
What Are the Main Types of Hydraulic Actuator?
Hydraulic actuators can be grouped into two broad motion categories:
- Linear hydraulic actuators – produce movement in a straight line
- Rotary hydraulic actuators – produce rotational movement
Hydraulic cylinders are the most familiar form of linear hydraulic actuator.
Rotary movement may be produced using hydraulic rotary actuators or hydraulic motors, depending on the movement required and the application.
Linear vs Rotary Hydraulic Actuators
| Actuator Type | Movement | Typical Component | Typical Use |
|---|---|---|---|
| Linear | Straight-line movement | Hydraulic cylinder | Lifting, pushing, pulling, clamping and positioning |
| Rotary | Limited or controlled rotation | Hydraulic rotary actuator | Turning, indexing, pivoting and positioning |
| Continuous Rotary | Continuous rotation | Hydraulic motor | Driving wheels, drums, conveyors, winches and rotating machinery |
Are Hydraulic Cylinders Actuators?
Yes. A hydraulic cylinder is a linear hydraulic actuator.
It converts hydraulic pressure and flow into straight-line force and movement.
Common hydraulic cylinder arrangements include:
- Single-acting cylinders
- Double-acting cylinders
- Single-rod cylinders
- Double-rod cylinders
- Telescopic hydraulic cylinders
- Special-purpose cylinders
Hydraulic cylinders are widely used because linear force is needed in many machines for lifting, pressing, extending, retracting, clamping and positioning.
For more information on multi-stage designs, see our guide to telescopic hydraulic cylinders.
Simple Definition
If a hydraulic component uses pressurised fluid to push or pull something in a straight line, it is performing linear hydraulic actuation.
What Is the Difference Between Single-Acting and Double-Acting Hydraulic Cylinders?
A single-acting hydraulic cylinder is hydraulically powered primarily in one direction.
Return movement is normally provided by gravity, a spring or another external force.
A double-acting hydraulic cylinder uses hydraulic pressure to control movement in both directions.
This allows the actuator to extend and retract hydraulically.
The correct arrangement depends on the machine, load, required control and operating conditions.
What Is a Hydraulic Rotary Actuator?
A hydraulic rotary actuator converts hydraulic energy into controlled rotational movement.
Unlike a hydraulic motor, which is normally selected when continuous rotation is required, a rotary actuator is commonly used where a component needs to rotate or pivot through a defined range.
Different internal designs can be used to convert hydraulic pressure into rotary output, including vane, rack-and-pinion and helical mechanisms.
Applications can include:
- Boom or attachment positioning
- Material-handling equipment
- Agricultural machinery
- Construction equipment
- Marine equipment
- Industrial positioning systems
Is a Hydraulic Motor an Actuator?
Yes. A hydraulic motor is a type of rotary hydraulic actuator that converts hydraulic energy into mechanical rotational output.
Hydraulic motors are normally used where continuous rotation is required.
Common hydraulic motor technologies include gear, vane and piston designs.
Typical uses can include:
- Conveyors
- Winches
- Drums
- Vehicle or machine drives
- Rotating attachments
- Industrial machinery
What Are the Advantages of Hydraulic Actuators?
Hydraulic actuation is widely used where machinery needs controlled movement and substantial force or torque.
HIGH FORCE DENSITY
Hydraulic systems can generate substantial force from comparatively compact actuator packages.
CONTROLLED MOVEMENT
Valves and system controls can regulate actuator direction, speed and movement.
FLEXIBLE POWER TRANSMISSION
Hydraulic hoses and pipework allow energy to be transferred between the pump, control components and actuator around a machine.
WIDE APPLICATION RANGE
Hydraulic actuation can be applied to lifting, pressing, steering, positioning, clamping, rotating and driving functions.
What Are the Limitations of Hydraulic Actuators?
Hydraulic actuators are powerful and versatile, but reliable operation depends on the condition of the wider hydraulic system.
Potential disadvantages or maintenance considerations include:
- Hydraulic oil leaks
- Seal wear
- Contamination sensitivity
- Heat generation
- Hose and fitting maintenance
- Wear to cylinders, motors or rotary actuator components
- Efficiency losses caused by internal or external leakage
- The need to maintain pumps, valves, filters and fluid as well as the actuator itself
The Actuator Is Only Part of the System
Poor actuator performance does not automatically mean the actuator itself has failed. Insufficient pressure, restricted flow, valve faults, contaminated oil or other hydraulic-system problems can produce similar symptoms.
Why Is Hydraulic Oil Important to Actuator Performance?
Hydraulic oil transmits energy through the system, but it also contributes to lubrication, heat transfer and component protection.
The condition and specification of the hydraulic fluid can therefore affect actuator performance and service life.
Potential issues include:
- Contamination damaging seals and moving surfaces
- Incorrect viscosity affecting system response and lubrication
- Water contamination contributing to corrosion
- Excessive heat degrading hydraulic oil and seals
- Dirty fluid accelerating wear within valves, cylinders and motors
For more information, see our hydraulic oil viscosity chart and our guide to choosing between ISO 32 and ISO 46 hydraulic oil.
Where Are Hydraulic Actuators Used?
Hydraulic actuators are found wherever hydraulic power needs to produce controlled mechanical movement.
Applications can include:
- Construction machinery
- Excavators and lifting equipment
- Industrial presses
- Manufacturing machinery
- Agricultural equipment
- Waste and recycling machinery
- Marine systems
- Material-handling equipment
- Transport and mobile machinery
- Special-purpose industrial equipment
The actuator type is selected according to factors such as required movement, force, torque, stroke, speed, duty cycle and available installation space.
What Causes Hydraulic Actuator Problems?
Hydraulic actuator faults can be caused by wear inside the actuator or by problems elsewhere in the hydraulic circuit.
Common symptoms can include:
- Loss of force
- Slow or erratic movement
- External hydraulic oil leakage
- Internal leakage
- Drifting or failure to hold position
- Unusual noise
- Overheating
- Jerky operation
- Failure to extend, retract or rotate correctly
Possible causes may include:
- Worn seals
- Damaged cylinder rods or bores
- Internal motor or rotary-actuator wear
- Contaminated hydraulic fluid
- Valve problems
- Insufficient hydraulic pressure
- Restricted hydraulic flow
- Damaged hoses or fittings
Can Hydraulic Actuators Be Repaired?
Many hydraulic actuators can be repaired, depending on their type, condition and extent of damage.
Hydraulic-cylinder repair may involve:
- Seal replacement
- Rod repair or manufacture
- Gland and bearing replacement
- Barrel inspection or repair
- Machining damaged components
- Rebuilding and reassembly
Hydraulic motors and rotary actuators require assessment according to their specific internal design.
Diagnose Before Replacing
Before replacing an actuator, the wider hydraulic system should be considered. A valve, pump, hose, pressure or contamination problem can sometimes create symptoms that appear to come from the actuator itself.
Hydraulic Actuator Repair & Engineering Support
Completely Hydraulic provides hydraulic engineering support for cylinders, hoses, valves and wider hydraulic systems used in industrial and mobile equipment.
Our services include:
- Hydraulic cylinder and ram repair
- Hydraulic hose repair and replacement
- Mobile hydraulic engineering
- 24/7 on-site hydraulic support
- Hydraulic valve support
- Hydraulic fault diagnosis
- Industrial hydraulic servicing
Keeping Machinery Moving.
Quick Engineering Summary
FUNCTION
Converts hydraulic energy into mechanical motion.
LINEAR ACTUATION
Usually provided by hydraulic cylinders.
ROTARY ACTUATION
Can be provided by rotary actuators or hydraulic motors.
SYSTEM DEPENDENCE
Actuator performance depends on pressure, flow, valves, fluid condition and the wider hydraulic circuit.
COMMON USES
Lifting, pushing, pulling, clamping, positioning, rotating and driving machinery.
Related Hydraulic Guides & Services
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If a hydraulic cylinder, hose, valve or actuator system is leaking, moving incorrectly or failing to perform as expected, Completely Hydraulic can assess the fault and recommend the appropriate repair route.
Hydraulic Actuator FAQs
What is a hydraulic actuator?
A hydraulic actuator is a device that converts hydraulic energy into mechanical movement. It may create straight-line motion, as with a hydraulic cylinder, or rotational motion, as with a rotary actuator or hydraulic motor.
Is a hydraulic cylinder an actuator?
Yes. A hydraulic cylinder is a linear hydraulic actuator because it converts hydraulic pressure and flow into straight-line force and movement.
What is the difference between a hydraulic actuator and a hydraulic motor?
Hydraulic actuator is a broad term covering devices that convert hydraulic energy into mechanical motion. A hydraulic motor is one type of rotary hydraulic actuator and is normally used where continuous rotational movement is required.
What is a rotary hydraulic actuator?
A rotary hydraulic actuator converts hydraulic energy into controlled rotational movement. It is commonly used where machinery needs a limited or defined angle of rotation rather than continuous spinning.
How does a hydraulic actuator create force?
Hydraulic pressure acts over an internal effective area. In a cylinder, pressure acting on the piston creates force that moves the piston and rod.
What causes a hydraulic actuator to move slowly?
Slow actuator movement can result from restricted flow, pump problems, valve faults, internal leakage, worn components, contamination or other hydraulic-system issues. The complete circuit may need to be assessed.
Can hydraulic actuators be repaired?
Many hydraulic actuators can be repaired. Hydraulic cylinders are commonly rebuilt with replacement seals and repaired or manufactured components, while motors and rotary actuators require assessment according to their specific design.
Does Completely Hydraulic repair hydraulic cylinders?
Yes. Completely Hydraulic provides hydraulic ram and cylinder repair, machining, rebuilding and wider hydraulic engineering support for industrial and mobile machinery.