What Are Pneumatic Actuators?

Post By: Luke West On: 06-03-2023 Read Time: 5 minutes - Guides - Pneumatics

In a pneumatic system, the actuator is the part of the machinery that makes it move. It’s often called a pneumatic drive, air actuator, pneumatic cylinder or air cylinder. Pneumatic actuators can take various forms, such as linear slides, rotary vane pumps, bellows or grippers. Whatever type of linear or rotary actuator is involved, it’s powered by the pressure of compressed air.

What Are Pneumatic Actuators

Types Of Pneumatic Actuator

All types of pneumatic actuator are intended to produce motion, which can be either linear or rotational. Rotary pneumatic actuators generate torque in place of linear motion, by transferring a piston’s linear motion to a rotating component, or vice versa.

Cylinders With Rods

The pneumatic cylinder is the most commonly used type of actuator. It consists of an external housing, called a bore, that contains a piston and a piston rod. The typically barrel-shaped bore has two end caps, with ports on either or both caps for letting the compressed air into the cylinder bore. The head-end cap is designed for the piston to travel through it as it extends.

Cylinders with rods are used in many industrial automation applications, including pulling, pushing, clamping, pressing, lifting, holding, stopping, separating, and more.

Rodless Cylinders

Pneumatic cylinders can also be actuated without rods. The linear slide actuator has a piston mounted on a sliding carriage, which moves by means of a mechanical or magnetic coupling. Mechanical types can include ball-bearing or plain surface-bearing actuation. These bearings are carried within parallel guides to move the carriage from side to side, with the mechanical component attached to it laterally.

Rodless cylinders are commonly used in packaging and cutting applications, as well as assembly & material transfer, and manufacturing electronics.

Rotary Pneumatic Actuators

Rotary pneumatic actuators create motion by using compressed air pressure to drive an oscillating vane or a rack and pinion assembly. This transfers the linear motion into a rotary motion. Rack and pinion pistons are connected with a gear wheel which produces rotary motion in a centrally mounted shaft.

Rotary pneumatic actuators are commonly found in industrial applications like positioning, controlling valves, clamping, conveying and transferring parts.

Bellows Pneumatic Actuators

This type of pneumatic actuator has a simple design, with no moving mechanical parts. They consist of rubber bellows attached to two metal connecting plates. Bellows cylinders can be used as driving components when the flexible bellows are pressurised. If compressed air is applied constantly, they provide cushioning. But if a stroke action is required, they contract when the external air pressure differential forces the bellows to exhaust.

Pneumatic bellows actuators are most often used for raising and lowering applications, especially those with a short stroke and high load. They can operate underwater, and can be used for compressing solids out of liquids such as sludge, as well as for damping vibration.

Increasing the pressure differential creates controlled kinetic movement. Double-acting pneumatic cylinders move the piston in both directions with compressed air. Single-acting cylinders move the piston in onssed air, using a spring assembly to return it to its original position.

What Are Pneumatic Actuators

How Do Pneumatic Actuators Work?

Compressing air builds up its pressure to create force, which the actuator converts into motion. This mechanical motion, in turn, usually regulates some kind of ultimate control element, such as valves, dampers, louvres, etc. A pneumatic actuator is therefore the particular piece of equipment which makes that conversion.

Pneumatic actuators may be designed to produce either linear or rotary motion. In the most common linear actuators, the external force of compressed gas or air is used to transport a load in a straight line. The actuator creates this force by driving a piston along inside the barrel of a hollow cylinder to build up a pressure much greater than the atmospheric pressure outside the cylinder. The linear force this action generates can be calculated by multiplying the surface area of the piston by its pressure differential.

Increasing the pressure differential creates controlled kinetic movement. Double-acting pneumatic cylinders move the piston in both directions with compressed air. Single-acting cylinders move the piston in only one direction with compressed air, using a spring assembly to return it to its original position.

Piston

The piston is a disc-shaped component inside the cylinder bore. It travels in a straight line back and forth (or up and down), acting as a movable partition. When compressed air is let into the bore via the inlet port situated on the rear-end cap, it pushes on the piston. The force of the compressed air makes the piston move away from its starting position and drives the piston rod out of the cylinder, where it’s attached to the moving parts of the machinery. This action is known as positive or plus (+) movement, so the pressurised chamber where this movement is initiated is called the plus (+) chamber. There is, of course, a minus (-) chamber on the opposite side of the cylinder.

Single Or Double-Stroke Piston

Once it has completed its forward motion, the piston goes back to its original position. How it does this depends on the piston type. If it’s a single-acting cylinder, the piston is usually pushed back by a spring on the front-end cap. When the cylinder is operating in a vertical plane, the piston may be forced back by gravity. If it’s a double-acting cylinder, then compressed air will be let in through another entry port to push the piston back with pneumatic force.

Bellows And Vanes

Other forms of pneumatic actuator movement include inflatable bellows or rotary vanes. Bellows-based actuators apply the force of compressed air directly to an inflatable membrane, which then displaces the air behind it to create forward (or upward) motion. Like cylinders and slides, bellows actuators have a rigid housing and end caps, but since they are frictionless, they require no lubrication. Bellows actuators can be single or double-acting if they are inflated from both directions.

Rotary vane actuators work in a similar way. A shaft-mounted vane is installed as a movable partition in a circular chamber. Compressed air is introduced to move the vane by differential air pressure in a rotary or pendulum motion, which turns the shaft to drive mechanical parts. The vanes can be single, or double with input and output ports on both sides so the rotation can go in both directions.