This article was updated March 17, 2023. It was originally published April 16, 2015.
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It seems almost all industries use linear actuators in some way—perhaps to move inventory, products, or components, or to carry out manufacturing and assembly processes. They convert energy into a motion or force and are usually powered by one of three methods: hydraulics, pneumatics or electricity. Here’s a quick look at each of these methods.
Pneumatic actuators have a piston inside a hollow cylinder that is moved through that cylinder by pressurized air entering from a compressor or pump. This linear motion can move a load or create a force. The piston returns to its original position using a spring or pressurized air supplied to the other side of the piston.
Most aluminum pneumatic actuators carry a maximum pressure rating of 150 psi. They are available in bore sizes from ½ to 8 in. and can create 7,500 lb. of force. For higher forces, steel actuators have a maximum pressure rating of 250 psi with bore sizes from ½ to 14 in. They generate from 50 to 38,465 lbf.
Accuracy. Pneumatic actuators routinely have positional errors of 0.1 in. and repeatability within .001 in.
Temperature resistance. Pneumatic actuators can withstand temperatures from −40°F to 250°F (−14°C to 120°C).
Safety. Pneumatic actuators do not use hazardous materials, so they pose no environmental or health hazards. They also do not use a motor so there is no possible magnetic interference, which lets them meet requirements for explosion protection and machine safety.
Low cost. The lightweight, durable actuators cost less than comparable hydraulic and electric versions. They also require little maintenance.
Compressed air. Pressure losses and air’s compressibility make pneumatics less efficient than other hydraulics and electricity. Compressor and air delivery can limit operations with lower pressures, resulting in lower forces and speeds.
The compressor must run and provide operating pressure even if nothing is moving. And even though the air is easily available and free, it must be kept clean and at the proper humidity; if it gets contaminated by oil or lubrication, it will lead to downtime and maintenance. Compressed air is a consumable that must be paid for, and the air lines and compressor must be maintained.
Hard to upgrade. Pneumatic actuators must be sized for a specific job to be efficient; they cannot effectively be used for other applications. And if a factory wants to improve control and efficiency, technicians must install proportional regulators and valves—a costly and complex upgrade.
Hydraulic linear actuators operate similarly to pneumatic actuators, but a pressurized incompressible liquid (hydraulic fluid) supplied by a pump rather than pressurized air moves the cylinder.
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