Pneumatic Rotary Actuators Information

Last revised: November 23, 2024

Reviewed by: Scott Orlosky consulting engineer

Pneumatic rotary actuators use pressurized air to rotate mechanical components to perform specific functions. They are used in applications such as machine loading and unloading, material handling, product assembly, welding, packing, testing and quality control.

Types of Pneumatic Rotary Actuators

Specifications

Operating pressure range and operating temperature are expressed as full-required ranges.

Maximum torque, the required range of torque output, if often measured in inch-pounds (in-lbs).

Rotational elements for pneumatic rotary actuators include shafts and tables. Shafts are circular and often include a keyway. Single shafts provide outputs on one side of the actuator. Double shafts provide outputs on both sides.

Rotating tables often include a bolt pattern for mounting other components. Shaft diameter or table diameter and shaft length or table height are important considerations. With output tables, the height or thickness does not include the actuator body.

Axial load and radial load are measured in pounds (lbs).

Linear stroke, the distance between the fully retracted and fully extended rod positions, is measured in inches (in). 

Rotation angle, the angle to which an actuator can rotate before reaching its travel limit, varies widely among pneumatic rotary actuators. Common rotation angles are 45°, 90°, 120°, 135°, 180°, 225°, 270°, 325°, and 360°. Pneumatic rotary actuators with rotation angles less than 45° or greater than 360° are also available.

Features   

                                                

Devices with an adjustable angle of rotation can be adjusted via screws or other stop features on one or both ends of the angular stroke.

Devices with stop cushioning contain air, a mechanical cushion, or a pad to soften the stop.

Pneumatic rotary actuators that provide positional feedback include encoders or potentiometers.

Some pneumatic rotary actuators include a closed loop air/oil system for hydraulic-like smoothness.

Position actuation can be accommodated by surrounding the output shaft with a magnetic strip or band that can be read by a switch.

Pneumatic Rotary Actuators FAQs

How do different types of pneumatic rotary actuators differ in terms of performance and applications?

Rack-and-Pinion Actuators: These are commonly used for applications requiring several complete revolutions. They are suitable for larger actuators in the process industry, such as operating quarter-turn valves.

Scotch Yoke Actuators: A mechanical device that converts linear motion to rotary motion or vice versa. Typically limited to 90 degrees of rotation, these are used for applications where a compact design is beneficial.

Rotary Vane Actuators: These can achieve up to 270 degrees of rotation and are often used for smaller loads.

Speed and Precision: Pneumatic actuators generally offer quick and efficient movement, which is crucial for applications requiring high-speed automation.

Durability: They are robust and can withstand harsh conditions, such as extreme temperatures, dust, and moisture, making them reliable for long-term use.

Energy Efficiency: While pneumatic actuators are less energy-efficient compared to electric actuators, they are simpler and cheaper to maintain due to fewer moving parts.

Industrial Automation: Pneumatic rotary actuators are widely used in machining, assembly equipment, and conveyor systems where precise control and movement are necessary.

Hazardous Environments: They are preferred in environments with flammable media due to their safety advantages over electric actuators.

Process Control: In the process industry, they are used for operating valves, especially where fail-safe conditions are required.

What are the advantages of pneumatic actuators over electric actuators?

Pneumatic actuators are generally less expensive initially and have fewer moving parts, which makes them easier and cheaper to maintain compared to electric actuators.

They are robust and can withstand harsh conditions such as extreme temperatures, dust, and moisture, ensuring long-lasting performance and reducing the need for frequent maintenance.

Pneumatic actuators are commonly used in applications requiring fail-safe conditions. They are less expensive for fail-safe applications compared to electric actuators, which would require a battery backup for similar functionality.

Pneumatic actuators are preferred in environments with flammable media due to their safety advantages over electric actuators. They are commonly used in hazardous or explosive working areas.

They provide fast and efficient movement, which important for applications requiring high-speed automation and precise control.

What are the limitations of pneumatic actuators compared to electric actuators?

Pneumatic actuators are generally less energy-efficient compared to electric actuators. Electric actuators are known for their high levels of precision, control, and energy efficiency.

Electric actuators offer higher precision and control, which makes them suitable for applications requiring precise modulation and positioning. Pneumatic actuators, while quick and robust, may not provide the same level of precision as electric actuators.

Pneumatic actuators require a continuous supply of compressed air, which can be a limitation if the site does not have an adequate air supply system. In contrast, electric actuators can be powered by commonly available electrical sources.

Pneumatic actuators may face challenges in extreme temperature conditions. Low temperatures can cause air sources to condense and freeze, potentially blocking the air supply and causing the actuator to fail.

While pneumatic actuators are generally compact, the need for additional components like air compressors and piping can increase the overall space requirement compared to electric actuators, which might be more straightforward to install in certain environments.

What are the maintenance requirements for pneumatic rotary actuators?

Pneumatic actuators should be regularly inspected for wear, damage, or leakage. Keeping the actuators clean and free from dust and debris is essential to maintain their functionality.

It is crucial to ensure that the air supply system is functioning correctly. This includes checking for proper pressure and cleanliness of the air supply. Moisture in the air lines can pose a problem, so it is important to monitor and maintain the air quality to prevent condensation and freezing, which can block air supply lines and cause actuator failure.

Pneumatic actuators have several components that require maintenance, such as compressors, seals, valves, fittings, mufflers, lubricators, filter regulator lubricators, solenoids, and air tubing. Regular maintenance of these components is necessary to ensure the actuator operates efficiently.

Following the manufacturer's guidelines for maintenance is essential. These guidelines provide specific instructions on how to maintain the actuator and troubleshoot any issues that may arise.

Consider the environmental conditions where the actuator is used. Pneumatic actuators can handle a range of temperatures, but low temperatures can cause air sources to condense and freeze. Proper seals, bearings, and mounting designs can help extend the temperature range and prevent issues.

What are the advantages of pneumatic actuators in hazardous environments?

Pneumatic actuators are inherently safer in environments with flammable media because they do not rely on electricity. The risk is that an electrical system can throw a spark or overheat and cause a flammable gas to ignite. This makes them suitable for use in hazardous or explosive areas.

They are also commonly used in applications requiring fail-safe conditions. Pneumatic actuators with spring return mechanisms can provide fail-safe functionality, such as fail-to-close or fail-to-open valve positions, without the need for additional power sources like battery backups, which would be required for electric actuators.

Pneumatic actuators are robust and can withstand harsh conditions, including extreme temperatures, dust, and moisture. This durability ensures reliable performance in challenging environments, reducing the risk of failure and the need for frequent maintenance.

They are generally less expensive to maintain due to fewer moving parts and simpler construction compared to electric actuators. This can be particularly advantageous in hazardous environments where maintenance can be more challenging and costly.

What are some of the applications where pneumatic actuators are preferred?

Pneumatic actuators are widely used in machining, assembly equipment, and conveyor systems where precise control and movement are necessary. Their quick response time and durability make them ideal for high-speed automation applications.

In environments with flammable media, pneumatic actuators are preferred due to their safety advantages over electric actuators. They do not rely on electricity, which reduces the risk of sparks and ignition, making them suitable for hazardous or explosive areas.

Pneumatic actuators are commonly used in the process industry for operating valves, especially where fail-safe conditions are required. They are less expensive for fail-safe applications compared to electric actuators, which may require a battery backup for similar functionality.

Due to their robust construction, pneumatic actuators can withstand harsh conditions, including extreme temperatures, dust, and moisture. This makes them reliable for long-term use in challenging environments.

Pneumatic Rotary Actuators Media Gallery

 

References

GlobalSpec—Pneumatic Drives: System Design, Modelling and Control

Image credits:

Numatics, Inc. | OMEGA Engineering, Inc. | Rotomation, Inc.

 


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