In the field of industrial automation, hydraulic actuators and pneumatic actuators are two widely used types of power components. Are you struggling with which one is better for me?
This guide will deeply analyze the differences between the two from multiple aspects such as working principles, performance, and practical applications. We believe this will help you make the most informed purchasing decision.
What is a Hydraulic Actuator？
The hydraulic actuator is a device that converts hydraulic pressure energy into mechanical energy that can drive a load. According to the final output motion form, hydraulic actuators are mainly divided into two categories: one is hydraulic cylinders that achieve linear reciprocating motion. Another type is hydraulic motors that generate continuous rotational motion.
What is a Pneumatic Actuator?
The pneumatic actuator is a device that uses compressed air as a power source to convert the pressure energy of the gas into mechanical energy. Similarly, based on the output motion form, pneumatic actuators are mainly divided into types such as cylinders that achieve linear reciprocating motion, as well as swing cylinders or pneumatic motors that output torque.
Hydraulic Actuator vs Pneumatic Actuator: Working Principle
How does a Hydraulic Actuator Work?
Firstly, the hydraulic pump pressurizes the hydraulic oil. These high-pressure liquids are guided into the actuator through pipelines and various control valves. Due to the almost incompressible nature of hydraulic oil, it creates a pressure difference and generates thrust on both sides of moving parts such as pistons, plungers, or blades.
This force will push the piston and piston rod to produce linear motion, or drive the rotor of the hydraulic motor to produce rotational motion. Subsequently, the hydraulic oil flows out from the other side of the actuator and returns to the reservoir, allowing the system to recycle and utilize the oil continuously.
How does a Pneumatic Actuator Work?
When the compressed air enters the chamber inside the actuator through the pipeline and control valve, there is a pressure difference in the chamber. This pressure difference acts on the piston or diaphragm inside the actuator, causing it to generate force and displacement.
Different types of pneumatic actuators will convert the pressure difference into different forms of mechanical motion.
In a linear pneumatic actuator, air is pushed into one side of the cylinder, which then drives the piston to move along the axial direction. The rack-and-pinion pneumatic actuator will convert the linear motion of the piston into rotational motion.
Hydraulic Actuator vs Pneumatic Actuator: Output Force
Hydraulic Actuator
The hydraulic actuators typically generate very large output forces. Hydraulic systems often operate at pressures of 3000 PSI (approximately 210 bar) or even higher. Because hydraulic oil is almost incompressible, this high pressure can be converted into thrust with very high efficiency.
Therefore, when the sizes are similar, the output force of the hydraulic actuator is higher than that of the pneumatic actuator. Because high-pressure oil can transfer more energy in a smaller space, hydraulic actuators have a much higher power density per unit volume or weight than pneumatic actuators.
This high force output characteristic makes the hydraulic actuator remain stable even when dealing with heavy loads, requiring large thrust or high torque.
Pneumatic Actuator
Compared with hydraulic actuators, the output force of pneumatic actuators is lower. The power density of pneumatic actuators is also lower than that of hydraulic actuators.
Most compressed air systems only provide a working pressure of 80 to 100 PSI (approximately 5.5 to 7 bar). This means that in order to generate a greater thrust, you must use cylinders with an extremely large diameter.
The compressibility of air leads to certain losses during the process of pressure transmission. When the load changes, the air pressure inside the actuator is prone to fluctuations, resulting in unstable output force.
Hydraulic Actuator vs Pneumatic Actuator: Speed
Hydraulic Actuator
The operation of the hydraulic actuator is slow. The hydraulic oil has a certain viscosity and will generate resistance when flowing in pipelines. The control valves of the hydraulic system have a relatively smooth response speed.
Therefore, the startup, direction change and operating speed of hydraulic actuators are generally slower than those of pneumatic actuators.
Pneumatic Actuator
Pneumatic actuators are usually capable of achieving very fast response and movement speed. The flow resistance of compressed air is low, and it can transmit quickly in pneumatic circuits.
With the rapid switching of the directional valve, the pneumatic actuator can quickly complete the actions of starting, stopping and reversing.
Under no-load or light-load conditions, the movement speed of pneumatic actuators is much higher than that of hydraulic actuators, and the action frequency can reach a dozen times per minute.
Hydraulic Actuator vs Pneumatic Actuator: Accuracy
Hydraulic Actuator
Hydraulic oil is incompressible and is less affected by load changes during motion. Combined with high-precision control components such as proportional valves and servo valves, you can accurately control the oil flow rate and pressure.
This makes the hydraulic actuator have high positioning accuracy and speed control capabilities. Even under varying load conditions, the accuracy degradation of hydraulic actuators is minimal.
Hydraulic actuators can meet the strict requirements of high-precision machining equipment, precision testing instruments, and other scenarios.
Pneumatic Actuator
The accuracy of pneumatic actuators is limited by the compressible physical properties of air.
When the load changes or the pressure fluctuates, compressed air is prone to volume deformation. This will result in a deviation between the actual displacement of the actuator and the theoretical value, making it difficult to achieve high-precision positioning.
Although you can assist in positioning by installing components such as electrical proportional valves, their cost is high and they are still not as stable as hydraulic systems.
Pneumatic actuators are more suitable for situations that do not require high positional accuracy but require fast point-to-point movement, such as material pushing or sorting.
Hydraulic Actuator vs Pneumatic Actuator: Structure
Hydraulic Actuator
The structure of hydraulic actuators is usually complex and contains more components. A complete hydraulic system includes actuators, hydraulic pumps, oil tanks, filters, various control valves, and other components. Each component is connected through a high-pressure pipeline to form a closed loop.
The hydraulic system has extremely high requirements for pipeline sealing to prevent high-pressure leakage. Due to the need to withstand high-pressure conditions, key components such as the cylinder body and piston of hydraulic actuators are usually made of high-strength alloy materials.
Pneumatic Actuator
The structure of the pneumatic actuator is relatively simple and lightweight. Pneumatic actuators are mostly made of lightweight materials such as aluminum alloy.
The pneumatic system mainly consists of actuators, air compressors, air storage tanks, filters, control valves, and other components. They are connected through low-pressure pipelines and do not require specialized return air pipelines.
Due to the low air viscosity and pressure, the sealing requirements for pneumatic pipelines and components are not as strict as those in hydraulic systems.
Hydraulic Actuator vs Pneumatic Actuator: Maintenance
Maintenance of Hydraulic Actuators
The maintenance of hydraulic actuators has the characteristics of high frequency and high professional requirements. Its maintenance focus is to maintain the cleanliness of the hydraulic oil.
You need to regularly check the cleanliness and viscosity of the oil. Replace the filter element and hydraulic oil promptly to prevent component wear or pipeline blockage caused by oil contamination.
At the same time, you need to regularly check the condition of the seals to prevent leakage. You also need to maintain components such as hydraulic pumps and radiators to keep proper heat dissipation and stable pressure in the system.
The maintenance process of hydraulic actuators usually requires professional technicians to operate and it is quite costly.
Maintenance of Pneumatic Actuators
The daily maintenance of pneumatic actuators mainly focuses on the treatment of the air source. You need to regularly drain the condensate water from the gas storage tank and filters to prevent rusting of components and clogging of pipelines.
Replace the filter elements regularly to keep the incoming air clean and dry. At the same time, you should check the airtightness of the pipe joints and seals to prevent any air leakage. Ordinary staff can complete the maintenance of pneumatic actuators after a brief training.
Hydraulic Actuator vs Pneumatic Actuator: Application
The Application of Hydraulic Actuators
Hydraulic actuators are often used in working conditions that require a large output of force, withstand extremely high loads, or require precise motion control. For example:
- Engineering machinery: The boom of the excavator extends and retracts. The lifting mechanism of a crane. The stamping action of a press machine.
- Metallurgical industry: Roll adjustment for steel rolling mill. The tilting and lifting device of the steelmaking furnace.
- Aerospace: Retraction and extension of aircraft landing gear.
- Manufacturing industry: Machine tool feed system.
- Architectural shading: Wind-resistant bottom-up zip screen lifting systems.
The Application of Pneumatic Actuators
Pneumatic actuators play an important role in many automation and manufacturing processes. Due to the use of clean air in the pneumatic system, even if there is a leak, it will not contaminate the product like hydraulic oil. It is very suitable for applications with fast movement, frequent cycling, and light loads. For example:
- Light industry automated production line: Sorting of electronic components. The conveying mechanism of food packaging equipment. Paper transportation in printing factories.
- Valve control: Opening and closing of ball valves and butterfly valves in water supply pipelines and ordinary chemical pipelines.
Hydraulic Actuator vs Pneumatic Actuator: Advantages and Disadvantages
Hydraulic Actuator
Advantages
- The hydraulic actuator can provide a powerful and stable output force.
- The hydraulic actuator operates smoothly and can achieve high-precision speed regulation and positioning.
- Even in the event of a power outage or pump station shutdown, the hydraulic actuator can maintain heavy objects without displacement for a long time.
- Hydraulic oil itself is an excellent lubricant. During the operation of the system, the flowing oil can provide continuous lubrication for the moving parts.
Disadvantages
- Hydraulic oil leakage can cause safety accidents and environmental pollution.
- The structure of hydraulic actuators is complex, with a larger volume and high maintenance requirements.
- The viscosity of hydraulic oil is greatly affected by temperature. You also need to configure additional heating or cooling devices.
Pneumatic Actuator
Advantages
- Pneumatic actuators have a simple structure, light weight, and few system components.
- The pneumatic actuator has a fast response speed. It can achieve very high actuation speed and cycle frequency.
- Air itself does not generate electric sparks and does not generate heat during operation. Pneumatic actuators are particularly suitable for use in harsh working conditions such as flammability and explosiveness.
- Pneumatic actuators do not have high requirements for environmental temperature. It can work stably in high and low temperature environments.
Disadvantages
- The working pressure of the pneumatic system is relatively low, which limits the output force of the pneumatic actuator.
- Due to the compressibility of air, the positioning accuracy of pneumatic actuators is relatively low. Fluctuations are prone to occur when the load changes.
- The production of compressed air requires an amount of electricity. Due to the heat loss and leakage during the gas compression and transportation, the overall energy utilization rate of pneumatic systems is usually low.
You can make a quick comparison by referring to the table below.
| Hydraulic Actuator | Pneumatic Actuator | |
| Power medium | Hydraulic Fluid | Compressed Air |
| Output performance | High thrust, high torque | Low thrust, low torque |
| Speed | Slow, steady | Quickly |
| Control Accuracy | High | Low |
| Maintenance | Complex | Simple |
| Application | Overload, high-precision control | Automation, rapid movement, and cleanliness requirements |
Hydraulic Actuator vs Pneumatic Actuator: How to Choose？
Clarify the Load Requirements
You first need to evaluate the required strength or torque. Choosing according to your actual load can avoid insufficient system power or excessive design.
Hydraulic actuators are suitable for handling high-load tasks. On the contrary, pneumatic actuators are suitable for action requirements ranging from light to medium loads. It outputs less force under low pressure, but it is sufficient for general operating conditions.
Action Speed and Control Accuracy
You also need to consider the requirements for motion speed and control accuracy.
Pneumatic actuators can achieve higher cycle frequencies and rapid responses because of their lighter gas medium and faster response. Hydraulic actuators can provide more stable control and precise positioning performance due to their fluid characteristics.
Working Environment
The environment also has a significant impact on the selection of actuators. In industries such as food, pharmaceuticals, and electronics, which have strict requirements for cleanliness, the pollution-free exhaust feature of pneumatic actuators makes them even more favored.
There is a risk of oil leakage and environmental pollution in hydraulic actuators. The performance of hydraulic oil will be affected in high and low temperature environments. You should consider carefully.
Cost and Maintenance Requirements
You need to take into account the full lifecycle cost, including the initial investment and maintenance costs.
The pneumatic actuator system has a simple structure. Its initial investment is relatively low and maintenance requirements are simple. The hydraulic system, due to its components such as hydraulic oil, pumps, and control valves, requires relatively extensive maintenance work and incurs higher costs.
Based on your budget and maintenance capabilities, making a reasonable choice can avoid high long-term operating costs.
FAQs
Is there a Pneumatic-Hydraulic Hybrid Actuator that Combines the Advantages of both?
Yes. The hydropneumatic actuator is an existing device. It combines the fast response of pneumatic and the high output and smoothness of hydraulic.
It uses a large-area pneumatic piston to drive a small-area hydraulic piston. By using the area ratio to increase the pressure, a very high hydraulic output can be achieved with a relatively low air pressure.
The hydropneumatic actuator is often used in processes that require quickly approaching the workpiece and then applying force slowly and smoothly, such as stamping or press-fitting operations.
Why is it sometimes Necessary to Provide Oil Mist Lubrication for Pneumatic Actuators?
Adding a small amount of lubricating oil to the compressed air to form oil mist is mainly to continuously lubricate the moving parts inside the actuator, such as the piston and the sealing ring. This can reduce friction and wear, prevent premature aging and cracking of seals, and help remove small amounts of impurities.
What are the Possible Causes of Leakage or Vibration in Hydraulic Actuators?
The vibration might be caused by misalignment of the transmission components. Leakage is usually caused by the wear and aging of the sealing components. By inspecting the internal sealing ring and related connections of the actuator, you can identify the problem and take measures such as replacement or adjustment to solve it.
Final Thoughts
There is no absolute superiority or inferiority between hydraulic and pneumatic actuators. The different characteristics of the working medium determine the performance of each. The final selection still needs to be matched according to your specific application scenario. If you have any further questions about hydraulic and pneumatic actuators, please feel free to contact us.
