An actuator is a device that converts energy into motion or is used to apply force. The device takes energy from a source -- which could be energy created by air, liquid, or electricity -- and converts it into the desired motion. The two basic desired motions are linear or rotary motions, but oscillatory motions are also common.
Linear actuators work by converting energy into straight-line motions, which serve a push or pull function. Rotary actuators, on the other hand, convert energy into rotational motions and commonly are used in various valves such as ball and butterfly valves.
Actuators typically are used in industrial and manufacturing applications. They are heavily relied upon by devices such as pumps, switches, motors, and valves. Each type of actuator has different versions and comes in many sizes, styles, and modes of operation, depending on the specific application.
Different types of actuators
Actuators are categorized by the energy source they utilize to generate motion. For example:
• Pneumatic actuators utilize compressed air to produce the desired motion
• Hydraulic actuators use liquid to generate motion
• Electric actuators use an external power source, such as a battery, to produce motion
• Thermal actuators use heat or magnetic energy to produce the desired motion
Mechanical actuators work by converting one type of motion (say a rotary motion) to another motion (a linear motion, for example). These actuators use a combination of components to operate, including gears, pulleys, chains, springs, and rails, among others.
A simple example of a mechanical actuator in operation is a chain block with gears being used to hoist a load from the ground up. The mechanical motion of the chain moving over the gears creates an upward linear motion, pulling the load up.
Pneumatic actuators are perhaps the most common type of actuator. They are powered by compressed air, which is used to move a piston when the air is released or uncompressed. Piston pneumatic actuators are commonly used to operate butterfly valves.
Pneumatic actuators are desired in many applications because they can quickly respond to start-stop operations, and also because they also don’t need a power source to operate. They are also cheaper, safer, more powerful, and more reliable than other actuators.
Hydraulic actuators utilize liquids such as oil to produce linear, rotary, or oscillatory motions. Unlike air, liquids are nearly impossible to compress, and therefore hydraulic actuators are used in applications where immense force is required. They are used in all systems that deal with high loads, such as heavy-duty construction equipment and ships.
Electrical actuators are one of the cleanest, easy-to-use, and readily available actuators because they do not use oil or call for compressed air for operation. Instead, they rely on energy from an external power source, such as a battery, to drive a motor and convert electrical energy into mechanical force. Motor operated electric actuators are used in large diameter pipelines.
There are also solenoid electrical actuators that are used for on/off purposes in valve systems that require frequent emergency shutdowns.
Thermal actuators use thermal or magnetic energy to produce the desired motion. They are lightweight, highly economical, and provide high-power density.