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The next time you see the jaws of an alligator figure open and snap shut or a haunted house monster reach for you as you pass by, chances are you are seeing a pneumatic actuator in action. There’s also a very good chance a retaining ring is being used to hold the important components of this assembly together, making all that scary action possible.

This pneumatic rotary actuator uses retaining rings on

both the front and rear of the application in order to

control the oscillating rotor.


Pneumatic rotary actuators are commonly used to convert compressed air pressure (in the form of a cylinder stroke) into an oscillating rotary motion. Like other pneumatic components, they are durable, offer simplicity

and high force for their size, and can operate in hazardous environments.


A common actuator design consists of a piston with teeth on the underside. These mesh with complementary teeth machined along the circumference of a shaft. Compressed air is forced into one side of the cylinder which moves the piston in a linear direction, engaging the teeth of the shaft, thus converting it to a circular motion. This motion can be in a clockwise or counterclockwise direction depending on which side of the actuator the compressed air is introduced.


Both of these movements can be used to create a “back and forth” motion for applications requiring such movement. So when the arm of the simulated executioner lets his ax fall, the 180 degree movement of the ax from a vertical position to the neck of the hapless victim then back again

can be accommodated through use of a pneumatic actuator.


Pneumatic actuators are used extensively in a variety of industrial applications as well. Some examples include powering brushes to clean pulp from rollers in the paper making process, causing targets to move during combat training for soldiers, lifting and lowering safety gates around part stamping machine operations.


The smooth turning of the shaft is assured through the use of a bearing, which in some applications can be subject to a significant axial load. In the actuator shown, design engineers selected an internal retaining ring

to accomplish the important task of bearing retention. This is a logical choice since, like the actuator itself, it is made to function in tight spaces and to reduce weight and costs associated with other more costly fastener

methods. The ring requires machining a simple groove, which can be accomplished with other production processes, further adding to the savings.




Learn more about all of our Retaining Rings here:


Download the rest of our Application Notes series here:


The Flexible, Versatile Retaining Ring


Retaining Rings Cure Fastener Concerns in Another Medical Application


Don't Discard That Leftover Retaining Ring



The jaws of many robotic alligator figures are controlled by these pneumatic rotary actuators.