There are many factors to consider as you work through choosing the appropriate pneumatic cylinder for your application. While some may be more obvious than others, it’s important to assess each of your application’s specific needs in order to ensure that you are implementing the right equipment into your system.
When the SS body disposable cylinder was developed, many people questioned the viability of a non-repairable product. This product has not only succeeded, it has also revolutionized the market. Because of its low cost and ease of replacement, many organizations opted to replace many traditional steel, aluminum and brass body cylinders that could be repaired. While these pneumatic cylinders are the most cost-effective choice and easiest to use, they do have limitations that make them less-than-ideal for certain applications.
Some applications require short cylinders, not allowing for the entire cylinder body to be much longer than its stroke. For these applications, compact or “pancake” cylinders available with round bodies or shaped aluminum extrusions are ideal. These cylinders use thin heads, caps and pistons. Short bearing surfaces keep cylinder length to a minimum. Because of their size, these pneumatic cylinders typically don’t resist side loads well and are not available in long stroke lengths. They are often used in clamping applications were space is at a premium.
Cylinders are designed to provide force on one axis. However, many applications experience forces that act on multiple axes, and cylinders must be able to operate at full capacity while resisting these lateral forces. The most common force attributed to pneumatic cylinder failure is side load. Side load consists of a force applied to the cylinder that is perpendicular to the active axis.
Certain types of cylinders are able to better withstand side load because they have longer bearing surfaces for the rod, longer pistons or a greater distance between pistons and the end of the rod bearing surfaces. Tie rod cylinders and the aluminum extruded version of square body pneumatic cylinders are more robust and better suited to resist side load. They can be built with stop tubes, which aid them in overcoming side load by increasing the distance between pistons and rod bearings surfaces, but add to overall cylinder length.
If you are looking to compensate for side load with lighter-duty cylinders, add guides parallel to the rod, which will absorb side load forces and allow for use in these applications.
Many lower cost cylinders available today are not built to be repaired. The crimped body disposable cylinder cannot be serviced, but low cost and versatility mean that it is easier to simply replace them rather than repair them. The ability to repair a cylinder and put it back into service quickly, however, is a great advantage in high-use MRO facilities. Hard cylinder components typically last through several seal changes, meaning that the ability to repair a cylinder can provide long-term benefits.
The number and type of cycles that cylinders experience are critical factors in determining the appropriate cylinders to use in your applications. High-cycle systems can wear out cylinder seals prematurely; as a result, high-cycle seals have been developed to extend cylinder life. Additionally, cylinders that reach the end of their strokes in normal system cycles experience reductions in life cycle resulting from continual piston impact absorption by these cylinders. To remedy this problem, cylinders are offered with cushions and bumpers to reduce force and extend cylinder life.
As the performance of aluminum and plastic cylinders have improved, people are opting to convert their steel pneumatic cylinders to ones made of these new materials. There are still applications, however, that demand the durability and serviceability that steel body cylinders provide. In heavy-duty applications such as those found in steel mills and foundries, long life provided by steel cylinders far outweighs any weight or cost savings found in lighter-duty materials. It is always best to process cautiously when deciding whether to replace steel with lighter-duty materials which many not always provide expected product life or serviceability in critical applications.
The environment in which cylinders operate may require specific types of cylinders. Some pneumatic systems run on lubricated air, which consists of in-line components that add oil mist to compressed air. This oil lubricates seals in valves and cylinders and reduces wear on elastomeric seals as they rub against cylinder walls or rods. Today, many cylinders and seals are matched to the type of compressed air that will be used in their respective systems.
Other environmental concerns involve outside issues that cylinders experience. These include extreme ambient temperatures, exposure to water or chemicals, vibration and debris on cylinder rods. Each of these issues can be addressed by choosing the proper cylinder. High- and low-temperature seals can be added to most series of cylinders, and some applications are extreme enough to warrant stainless steel tie rod cylinders that withstand caustic or corrosive environments. Rod scrapers can also be added to remove debris from rods before cylinder seals are damaged.
The key is to recognize the challenges that your specific application faces before you select your cylinder. This way, you can be assured that your choices will meet the needs of your application.
To learn more, contact your local Kaman Fluid Power to speak with a pneumatic specialist today.
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