Pneumatic cylinders are a type of mechanical appliance that makes use of power generated from compressed gas to create a force in reciprocating linear motion. They are also sometimes referred to as air cylinders, as in “pneuma” meaning air. Much like in hydraulic cylinders, a force is exerted into the piston which propels it towards the desired direction. In these devices, the piston is actually a cylinder or a disc, and the force developed by it is transferred by the piston rod to the object that is to be moved. Pneumatics is occasionally preferred by some engineers as they are much cleaner, quieter and doesn’t require much space for the storage of fluids.
Depending on the purpose for which they are used, these cylinders come in a variety of shapes and sizes. This is also applicable to the kind of material used to construct these cylinders. They can be made out of steel, stainless steel, aluminum and nickel-plated brass. Choice of materials is mostly dictated by the humidity, temperature, specific stroke length and the amount of loads. The body constructions in which these cylinders are available include the following:
- Flanged-type cylinders: In this type, fixed flanges are present at the ends of the cylinder.
- Tie rod cylinders: This is the most common form of cylinder construction and can be used for a wide variety of loads. It has also been proven as the safest form to work with.
- Threaded end cylinders: In this type, the ends are screwed to the tube body. However, reduced material may lead to weakening of the tube and introduce thread concentricity issues to the system.
- One-piece welded cylinders: In this type, the ends are crimped or welded to the tube. Although these are inexpensive, they make a cylinder non-serviceable.
There are different types of pneumatic cylinders in use in a wide variety of industrial and commercial arenas. Some of them have been discussed below in brief.
Single-acting cylinders or SAC makes use of pressure that results from compressed air to create a unidirectional driving force, usually towards the outside, and a springing motion to get back to its original position. In most cases, these cylinders have very limited extension because of the space taken up by the compressed spring. Another flip side of single-acting cylinders is that a portion of the force is always lost as it attempts to push itself against the spring.
Double-acting cylinders or DAC makes use of air pressure to move in extend as well as retract strokes. These cylinders are comprised of two ports which lets the air in; one for instroke and the other one for outstroke. The stroke length for double-acting cylinders is not limited. This type of cylinder is not however without its flaws. The piston rod may buckle and bend over time and precise calculations should be carried out before working with these cylinders.
Telescoping cylinders or telescopic cylinders come in either single-acting modes or double-acting modes. It makes use of a piston rod that is placed within a few hollow stages of ascending diameters. Once activated, the piston rod along with each of the successive stages “telescopes” out like a separate segmented piston. This type of pneumatic cylinder design allows for much longer strokes than what can be achieved by a single-stage cylinder of same retracted or collapsed length. However, its segmented piston design increases the chances for piston flexion. For this reason, these type of telescoping cylinders are mainly reserved for applications where its piston has to go through minimal side loading.
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