All about Pneumatic Rotary Actuators
When selecting the rotary actuator for your system, among the most important design considerations are mechanical efficiency, package size, shaft options, max rotation, and cost. Apart from these, you must also consider characteristics including backlash, load-stopping ability, and its ability to handle both axial and radial loads on the shaft. There are two main types of pneumatic rotary actuators: rack & pinion and vane actuators. This blog will explain both types, as well as their pros and cons.
Rack-and-pinion pneumatic valve actuators, also called limited rotation cylinders, are rotary actuators used to turn, open, close, mix, oscillate, position, steer and carry out other mechanical functions involving restricted rotation. These actuators are also often used for automation of quarter-turn valves, such as ball or butterfly valves. Pneumatic rack-and-pinion actuators convert the energy of compressed air through the use of a pneumatic cylinder to an oscillating rotary motion. The clean, dry, and processed gas required by this actuator is provided via a central compressed air station, which usually supports many pneumatic devices in a process system. Rack and pinion rotary actuators are ideal for high speed production applications and situations where low wear and long lifespan are important. This type of rotary actuator has a variety of pros and cons.
Pros
- Wide range of torque and rotation. These also deliver excellent mechanical efficiency, often up to 90-95%.
- Designed with a profile that makes mounting options more simple.
- Hollow pinion gears offer flexibility and allow the machine’s shaft to mount through the pinion gear of the actuator. This eliminates the need for a coupling.
- Able to accomodate large loads, unlike air cylinders, which provide force but do not support a load.
- One roller bearing assembly that supports both the pinion gear and axial loads
Cons
- Potential for backlash caused by a minute gap between the gears. This is not usually an issue for most applications because the gap is only about one degree.
- Wear on the gears is common in these, which causes backlash to increase over time. This can be prevented by using a double rack version, which eliminates backlash by imposing a counter force on the pinion gear.
Vane actuators are true rotary actuators that do not require the conversion of a linear motion to a rotary motion. This results in a simple, highly accurate and reliable quarter-turn pneumatic actuator that is suited to demanding process flow control applications. These are ideal for applications where space is limited. Vane actuators are often used to clamp, transfer, or position light loads in medium-speed applications. The pros and cons of vane actuators are as follows:
Pros
- Good mechanical efficiency from 75-85% due to the friction of the vane seals and shaft bearings.
- Minimal bypass leakage over the vane seals.
- No backlash, meaning positioning is precise.
- Less expensive, making it a good option for light to medium duty pneumatic applications.
Cons
- Limited rotation and torque range in comparison to rack and pinion actuators, typically up to 280° maximum for a single vane model. This means they are best suited to light loads in medium-speed applications.
- As the shaft utilizes small bushing-type bearings, they are only able to accommodate light loads.
- Limited shock capability compared to other actuators. Higher speed applications generally require external stops.
Once you determine what type of rotary actuator is best for you, the next step is to ensure you are getting them from a trusted source. For top quality rotary actuators and much more, look no further than ASAP Aviation Stock. Owned and operated by ASAP Semiconductor, we can help you find all types of parts pertaining to the aerospace, civil aviation, defense, industrial, and electronics markets. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, call us at 1-763-401-8616 or email us at sales@asapaviationstock.com.
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