What is a Pneumatic Actuator and what are some applications of different types?
An actuator is a device that makes something move, allowing for hands-off operations to be possible. Actuators are classified based on where they source their energy from, and actuators used in machinery are typically electric, hydraulic, or pneumatic. An electric actuator runs on electricity and can be found in an electric engine. A hydraulic actuator runs on incompressible oil, or hydraulic fluid, and can be found in the steering gear of a ship. Lastly, a pneumatic actuator compresses air and creates kinetic energy through movement, and such parts can be found across many applications. This blog will explore the diverse functions of pneumatic actuators in particular and the way actuators operate.
Pneumatic actuators are categorized by their motion, which can be either linear or rotary. Linear pneumatic actuators can move objects back and forth in a straight line. Meanwhile, rotary pneumatic actuators can move objects in circular motions. Common designs of linear pneumatic actuators include the spring/diaphragm style and the piston style. Both models depend on a spring within the cylinder that moves according to pneumatic pressure.
The difference between the models comes down to where the pneumatic pressure is being applied. In the piston model, the piston moves up or down based on pressure imbalances within the cylinder. This then compresses the spring. If the pneumatic source comes from below the spring, the piston moves up in an “air-to-retract” motion. If it instead comes from above, then the piston moves down in an “air-to-extend” motion. In the spring/diaphragm, pressure is applied directly to a diaphragm which is attached to a plate and an actuator stem. High pressure will push the diaphragm down, compressing the spring. The attached stem opens a valve and the default state of being open or closed in the absence of pressure can be decided by where the pressure supply is located relative to the diaphragm. The spring/diaphragm style is most common in control valves.
Common rotary style actuators include the rack and pinion style actuator and the vane style actuator. The difference between the two models is in the moving parts. The vane style actuator has a cane attachment similar to the shape of a handheld fan. The vane is mounted on a shaft which pushes it around in a circle. In the rack and pinion actuator, the piston moves in a linear motion, rotating a gear and driveshaft. An actuator can be used to produce specific currents of flow in your system and pneumatic actuators will function reliably for your control valve as long as you are fully informed of your operating conditions. Low pressure systems also employ the use of pneumatic power; however, they require less intense maintenance and have less complex materials. These systems might not require backup pressure bottles or bidirectional valves.
While pneumatic actuators are common for the aircraft systems that depend on pressurized air alone, hydraulic and electric actuators come into play as well in many important functions, such as in landing gear. Examples of actuator use can be found in aircraft in several applications, including landing gear, flaps, and autopilot systems. Many of the systems that depend on actuators feature high pressure values of around 3000 psi. One high pressure electric system is employed to power twin engines. Most actuators used for these purposes have four-way valves, which allows for the bidirectional flow of liquids and for an exhaust exit. In a twin engine system, when pressure surpasses 3,300 psi, the exhaust valve opens and drainage occurs in order to prevent a buildup of pressure. The towbar in landing gear might move up and down in some conditions to access the nose of the aircraft, and this motion is powered by hydraulic fluid. Selecting the proper actuator for your specific usage is important for making sure you can generate power.
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