Actuators are mechanical devices that take energy created by air, electrical power, or hydraulic fluid and convert it into some kind of motion — blocking, clamping, or ejecting motion, for example. Sometimes, actuators are used to apply a force. More specifically, they’re used in the manufacturing of machines and other equipment to initiate valves that stop or start a function. Actuators can be found in devices such as motors, pumps, and switches.
Actuators are typically categorized by the energy source they require in order to generate motion. There are numerous types of actuators available — pneumatic, electric, hydraulic, thermal, magnetic, and mechanical, to name just a few.
Below, we’ll focus on the pneumatic and electric varieties in particular.
The Basics of Pneumatic Actuators
Pneumatic actuators convert energy — typically, compressed air — into rotary or linear motion. The most common type of actuator, pneumatic models are essentially airtight cylinders, normally fabricated using metal. They use compressed air to move a piston when air is released or uncompressed. Pneumatic actuator applications are typically found in the manufacturing and assembly sectors.
Pneumatic valve actuators offer a range of benefits:
- They provide more force than any other actuator technology besides hydraulics
- They operate at high speeds
- They’re the most economical option when the scale of deployment matches the capacity of the compressor, and
- They’re typically less expensive and easier to maintain than other types of actuators.
However, acquiring a pneumatic system to drive an actuator can be quite costly. Also, in low-temperature applications, condensate may freeze and block air supply lines, rendering the actuator inoperative. To operate at peak efficiency, pneumatic actuators must be sized for specific jobs.
As mentioned previously, both rotary and linear pneumatic actuators are available. Specialty models are also available that combine both types of motion. Other types include grippers, tie rod cylinders, rodless actuators, and vacuum generators.
The Basics of Electric Actuators
Electric actuators utilize a motor to generate torque to operate valves in mechanical equipment. These actuators consist of a ball, Acme, or roller screw connected to an electric motor by a coupler. As the screw turns, it moves a piston connected to the rod or carriage that moves the load. Electric linear actuators, in particular, are typically used when equipment requires multi-turn valves, such as gate or globe valves. Electric rotary actuators are primarily used in automation applications when a gate or valve requires controlled movement to specific rotation positions.
Electric actuators allow for precise control and positioning, easy maintenance, and low replacement costs, as electronics are separate from the actuator. And compared to pneumatic actuator valves, they produce minimal noise. They can overheat, however, meaning they must be reliably sealed from moisture. In hazardous environments, they must be modified with a NEMA enclosure. The price tag for electric actuators can be prohibitive for many user applications.
Pneumatic Vs. Electric Actuators
Performance characteristics are often the key factors when deciding between pneumatic and electric actuators.
- Speed — Pneumatic actuators can operate at variable and very high speeds; electric actuators run at fixed, moderate speeds.
- Hazardous environment — Pneumatic linear actuators are explosion-, shock-, and spark-proof. As mentioned previously, electric actuators must be modified with a NEMA enclosure in hazardous environments.
- Overheating — Again, the advantage goes to pneumatic actuators, which aren’t subject to overheating and operate without issue in wet environments. Electric actuators, on the other hand, can overheat and must be sealed from moisture.
- Duty cycle — Pneumatic actuators operate with a 100% duty cycle; electric units have a 25% standard duty cycle that may be increased.
- Stalling — Electrical actuators, which cannot be stalled, have the edge here. Pneumatic actuators may be stalled indefinitely.
- Torque-to-Weight Ratio — There’s a high torque-to-weight ratio for pneumatic actuators, whereas electric actuators have a low torque-to-weight ratio.
- Spring Return — Pneumatic actuators have the upper hand here. Pneumatic varieties have a spring-return (i.e., fail-safe) option that’s practical and economical; this spring-return option is usually unavailable for electric actuators.
Selecting an Actuator Type
There’s a lot to consider when deciding whether to use a pneumatic or electric actuator. Each has inherent pros and cons, but the best option will depend on specific application needs, budgetary constraints, and performance requirements. Taking the time to thoroughly evaluate options will help ensure optimal actuator quality and longevity, keeping operations running smoothly and efficiently.