Pneumatic Actuator's Working, Types, and Applications.

20 Mar.,2024

 

The Pneumatic Actuator is an integral part of many control systems. But while that is so, it’s one of the less understood automation devices. That prompted us to write this article. In the article, we explain the meaning of the pneumatic actuator, how it works, its various types, and when or where to use it.

What is a Pneumatic Actuator?

A pneumatic actuator is a mechanism that uses air pressure to move, position, or control the operation of a device. “Pneumatic” means air-based, while “an actuator” is any device that causes something to move.

Depending on the type, a pneumatic force actuator may push a load, pull it along a straight line, or cause it to rotate. Its design also varies greatly, ranging from the simple to the complex. The most used mechanisms are:

  • A piston that moves inside a cylinder
  • A rotating vane in an enclosure
  • A flexible diaphragm inside a casing
  • A rack and pinion gear system

In the real world, air actuators have many applications. They can be the on/off mechanisms of flow-regulating valves or control the operation of automotive systems.

In factories, they form part of process control equipment such as material handling and packaging machines; the list is endless.

The operation of a pneumatic air actuator illustrated
Resource: https://www.youtube.com/watch?v=yCLm2hr02ZU

How Does a Pneumatic Actuator Work?

Pneumatic or air actuators turn the force of a compressed gas into linear or rotary motion. The motion then performs a valuable function, such as controlling the operation of a device or part of a system. Let’s see how that happens.

  • Compressed air or other gas enters the actuator housing through the supply port
  • Inside the housing, the air pushes against a piston, diaphragm, or vane, creating motion
  • Depending on the actuator design, the motion is along a straight line or a rotation
  • The compressed air moves out of the exhaust or other port
  • Air pressure reduces, and the moving component returns to its former position

A single-acting pneumatic actuator includes a return spring in its actuating assembly. The spring pulls back the moving part when air pressure is no longer acting on it. Double-acting types use compressed air for the return action.

Pneumatic actuator assembly components
Resource: https://www.researchgate.net

Pneumatic Actuator Parts

Different parts make up a pneumatic or air-operated actuator assembly. The main ones and their specific function include the following:

  • A flow control valve
  • Cylinder/housing
  • Rod or shaft, piston, or diaphragm
  • A return spring and several other smaller components.

Valve – the pneumatic actuator valve controls the flow of compressed gas as it goes into the cylinder or housing, allowing for variable actuator speed, torque, and other options.

Cylinder/Housing – the pneumatic actuator cylinder is the air-tight chamber that receives compressed gas. It contains a piston that moves under the action of air pressure.

Piston/Diaphragm/Vane – depending on the type of this device, a piston, diaphragm, or vane is pushed by pressurized air to cause motion.

Rod/Shaft – this part connects the moving piston, diaphragm, or vane to the load, transferring the air-generated motion.

Return spring – some types of air actuators, called single-acting actuators, use a return spring to retract the moving part when air vents out and pressure reduces.

Pneumatic actuator types
Resource: https://www.youtube.com/watch?v=MHlnTQV1Tn0

Types of Pneumatic Actuators

Air actuators are available in various design options. They are broadly categorized based on whether they produce a rotary or linear motion. Linear motion types are mostly piston and diaphragm-based, while rotary actuators use rack and pinion gears or vane assemblies.

1. Linear Pneumatic Actuator

In a linear air actuator, motion happens along a straight line. To produce the movement, air presses against the surface area of a movable piston. Alternatively, this can be a spring-loaded diaphragm connected to a rod.

Piston Pneumatic Actuator

In this type of actuator, a piston moves back and forth inside a cylinder. The piston connects to a rod, which, in turn, links it to the load (the part moved).

When compressed air enters the cylinder, its force causes the piston to move, and the actuator performs the required function. The pneumatic piston actuator can be single-acting or double-acting.

In the single-acting type, a return spring retracts the piston when air pressure reduces. The double-acting version uses pressurized air to perform the same function.

Pneumatic Diaphragm Actuator

The pneumatic diaphragm actuator comprises a flexible diaphragm inside a sealed enclosure and a moving rod or actuating stem. The single-acting type includes a return spring to pull back the diaphragm at the end of a stroke.

To produce the required movement, a control valve sends a compressed gas into the area above the diaphragm. The diaphragm, now under pressure, moves downward, compressing the spring and moving the stem.

At the end of the cycle, the air exhausts from the housing. The diaphragm is no longer under pressure. The spring releases its energy and pushes the diaphragm to its former position.

In some actuator versions, compressed air flows into the opposite side of the diaphragm to push it back. These do not require a return spring.

2. Rotary Pneumatic Actuator

The rotary type rotates a shaft and transfers motion to the actuating component. Most often, the device is a piston rack-and-pinion system or a vane assembly. Let’s see how each of these actuator types works.

Rack and Pinion Pneumatic Actuator

In this type, a movable piston connects to a rack and pinion gear. When pushed by a compressed gas, the piston moves the rack gear back and forth.

The moving rack then rotates the pinion gear, and this causes rotation. Like other actuators, this movement can move a load and perform a function.

Pneumatic rack and pinion actuators have varied applications in manufacturing systems. Other uses include the control of butterfly and ball valves of large pipelines.

Vane Type Pneumatic Actuators

These actuators use a moving vane mounted inside a sealed housing. The vane has a shaft connected to it. Introducing pressurized air into the housing causes the vane to move in one direction.

The vane then moves in the opposite direction when the air is released. The back-and-forth motion rotates the shaft and performs a desired function.

Vane-type pneumatic actuators are simple in construction, compact, and less demanding to maintain than other air actuators. They’re also low-cost and more reliable.

Examples of pneumatic or air actuators
Resource: https://youtu.be/FNeXt_buqWA?

Advantages and Disadvantages of Pneumatic Actuators

Like any other type of actuator, such as hydraulic or electric, the pneumatic actuator has both advantages and disadvantages. These should inform your choice, usually based on the intended application or device operating environment.

Advantages of Pneumatic Actuators

The advantages of pneumatic actuators are summarized below.

  • Rapid actuation/response time
  • Simple design and operation
  • excellent reliability i
  • Safe to use around flammable materials
  • Higher power-to-weight ratio when compared to other actuator types
  • Low cost

Disadvantages of Pneumatic Actuators

  • Low accuracy level
  • Affected by impurities, including condensation
  • Require the use of an air compressor
Pneumatic air actuator in an industrial setting
Resource: https://www.assemblymag.com

Pneumatic Actuator Applications

You can use a pneumatic or air actuator in many settings. It can be an actuator to open and close a valve, for example, or the mechanism of a power tool. Popular uses include those in the list below.

  • Material handling and process control equipment
  • Automotive and aerospace systems
  • In robotic systems to operate grippers, etc.
  • To automate the valves of wastewater, chemical, or oil and gas pipelines
  • Process and flow control in HVAC devices and systems
  • In the switching devices of power plants and other high-voltage systems

Pneumatic actuator manufacturers make all kinds of these devices. Typically, these include linear and rotary actuators. Based on the required function, one may use either type.

Conclusion

In automation and other controlled processes, actuators play the crucial role of creating motion and moving parts. The pneumatic actuator, in particular, is one of the most used types of these actuators and also one of the most versatile. It uses air under pressure to work and is available in many types, the most popular being piston and diaphragm or vane-based actuators.