Air-actuators, air cylinders: What do you need to know?

Air-actuators, air cylinders: What do you need to know?

 

Air-actuators / Air Cylinders; there are many definitions of the word actuator, most referring to "one who actuates".We did find one that relates more specifically to our needs: Air-actuators are

"A device that creates mechanical motion by converting various forms of energy to rotating or linear mechanical energy"

 

When we use an air-actuator we are converting the energy stored in our compressed air into mechanical energy. The compressed air ‘moves things’, usually by attaching them to a cylinder piston rod.


Types of Actuators

The type of actuator you will need for your application will depend on what it is you are trying to do and the range of motion desired. There are linear and rotary actuators commercially available. You can select electric or hydraulic actuators rather than air actuators; electricity and hydraulics being other readily available forms of industrial energy.

Electrical actuators have their place, though pneumatic actuators will provide more power in a smaller package at a lower cost than electrical actuators can. If yours is a high cycle speed application, electric actuators wouldn't be your first choice as they don’t normally provide the speed that an actuator driven by compressed air can. For precise positioning applications, the first choice is often electric actuators. They can provide positioning to tighter tolerances than most air cylinders. Also, where compressed air is not readily available, electric actuators can be the option of choice.

Hydraulic actuators are the champion when it comes to brute force, easily outperforming air cylinders of the same bore size. With hydraulics you can generate much more force from a much smaller actuator than is possible with air. This power to size superiority comes at a higher cost over pneumatic components. If it's high brute force - thousands of pounds of force - or you need to generate relatively high force in a smaller footprint – perhaps where there isn’t room for a pneumatic actuator of the size necessary to provide the force the application requires - hydraulic actuators are called for.

Generally though, if you can generate the force you need with air and the actuator footprint isn't the biggest issue, your application doesn't require precise positioning, then air cylinder actuators would be your first choice. They are easy to obtain, have simple operation and are relatively low cost.

Sizing

When sizing the air actuator for your application, you’ll need to understand this:

Force = Pressure x Area


Have a look at this page for more information on cylinder size to better understand how the formula F=PxA applies to air cylinders in general and the surface area of the cylinder piston in particular.

 

Once you know the surface area of the piston inside the air actuator, by knowing the air pressure that flows into the cylinder – air pressure being measured in pounds per square inch (PSI) - it is easy to calculate the theoretical force to be generated by that cylinder with that air pressure. It is force that is available theoretically only, as you will likely lose about 10% or so of the force that is available from a specific bore size cylinder just to overcome the friction created by the piston and rod seals inside itself.

Rule of thumb: Consider oversizing the air cylinder selected by at least 25% for your application, this to account for force loss to friction and to allow sufficient force-safety-margin when the cylinder is working.

Nothing about air cylinders or air actuators is complex, though there is lots of information about them and their uses.