If you’re trying to learn about air cylinders and what they are, you'll come across the word pneumatic often. If something is pneumatic, it contains or is operated by air or gas under pressure. Air cylinders are pneumatic systems that use compressed air to move a load. But how do they work?
What Are Air Cylinders?
To get a better understanding of what air cylinders are (and what they can do), it helps to freshen up a little on some science first. Pneumatic cylinders turn the potential energy of compressed air into mechanical energy. Mechanical energy is the sum of an object’s potential energy and kinetic energy.
Imagine a cylinder with a piston (or small disc) at the very left end. When compressed air is released through a valve at the left end, the air expands—or uses its full potential to move the piston (kinetic energy, or the energy of mass in motion) from the left end of the cylinder to the right.
The result of all that “work” is linear motion (the piston moving from one end to another). This motion makes it possible to open and close doors, push and pull items, or even lift objects. But how does the piston move back to its original position? It depends.
Single vs. Double-Acting Cylinders
In order to repeat the motion above, the piston must eventually return to its original position. There are two distinct ways this is usually achieved. The first one is called a single-acting cylinder. Single-acting cylinders have a single air port that forces the piston out, and an internal spring that springs the piston back to its original position.
The second option is called a double-acting cylinder. Double-acting cylinders have two air ports, one at each end. These ports move the piston by alternating which port receives the compressed air.
Control Air Flow in Air Cylinders
How do you slow down or speed up the flow of air in an air cylinder? There are two types of control valves that are built into (or sometimes added onto) a cylinder, to help regulate the flow of air. The first one is a needle valve. In a double-acting cylinder, adjusting a needle valve increases or decreases the flow of air in both directions. A flow control valve, however, allows you to restrict flow in just one direction.
To further increase the speed of a pneumatic cylinder, you can use a quick-exhaust valve. This allows the tank containing compressed air to rapidly depressurize, as opposed to forcing the air to travel back through an existing path.
For enhanced control overall, you can use speed control mufflers, which provide metered control. It’s worth noting that lubrication is not recommended for increasing speed. While bearings and chains associated with pneumatic systems may require lube, the system itself generally does not.
Controlling Pneumatic Pressure
Regulators exist in pneumatic systems to maintain constant pressure and minimize pressure levels to meet work requirements without wasting pressurized air. Methods for doing this include using differential pressure and dual pressure regulators. These methods are particularly relevant in double-acting cylinders where the pressure necessary to return the piston is significantly less than the pressure required to send it out. Employing pneumatic regulators can lead to more efficient systems.
Lubricating Pneumatic Systems
The lubrication of pneumatic systems is far less common than it used to be. This is because early systems used products like rubber or leather for seals. Lubrication existed to enhance the seal and reduce friction. However, modern systems employ synthetic materials that are more suited to the task. They also use additives like Teflon to improve overall lubricity and greases that help create long-lasting seals.
When working with older systems that do require lubrication, only apply the lube directly to the part that requires it. Lube caught in the system will vaporize and risk leaking out. This is especially essential to avoid in pneumatic systems that are used in areas for food service, due to the threat of cross-contamination.
Fully understanding pneumatic systems can require deep knowledge and training. But a basic understanding of how these systems work may help give you more control over the operation and improve your overall approach to maintenance.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.