Pneumatic Cylinders

What Are Pneumatic or Air Cylinders?

Pneumatic cylinders (sometimes known as air cylinders) are mechanical devices which use the power of compressed air to produce a force in a reciprocating linear motion. Like hydraulic cylinders, something forces a piston to move in the desired direction. The piston is a disc or cylinder, and the piston rod transfers the force it develops to the object to be moved. A cylinder consists of the following parts: Tube, either a profile or round. Back endcap and front endcap. Piston and piston seal Piston rod Piston rod seal Scraper When compressed air enters through the port in the back endcap, the piston moves away from the end cap and pushes the rod out. This movement is called the positive or plus movement and the chamber associated with this movement is called the plus chamber. The minus chamber is located on the opposite side. When compressed air enters the port in the front endcap the rod is pushed back to the negative position.

How to Measure a Pneumatic Cylinder

How Does a Double Acting Pneumatic Cylinder Work?

With double acting pneumatic cylinders air is supplied to chambers on both sides of the piston. Higher air pressure on one side can drive the piston to the other side. Double-acting cylinders are the most common type, as they give the user full control.

What are the Advantages of Double-Acting Pneumatic Cylinders?

The advantages of double acting cylinders are their longer strokes (up to several meters) and constant output force through a full stroke.

How to Calculate the Force from a Pneumatic Cylinder?

The formula force equals pressure times area is widely used in pneumatics. We use it to calculate the maximum force we can obtain from the cylinder in order to understand how heavy the objects are that we can move. With this formula, we can calculate either what size of cylinder the customer needs, or what pressure we need in order to move the object that he or she wants to move. Note that the area is not the same in the two chambers. Because of the piston rod we have a smaller area in the front, when the cylinder is retracting. That is why we have different forces depending on whether the cylinder is pushing or pulling.

How Does a Single-Acting Pneumatic Cylinder Work?

In a single acting cylinder, air is only supplied to one side of the piston and is responsible for the movement of the piston in only one direction. The movement of the piston in the opposite direction is performed by a mechanical spring. A single acting cylinder can be designed with base position minus (spring return) or base position plus (spring extend) depending on whether the compressed air performs the out stroke or the in-stroke respectively. In case of pressure or power loss, a single acting cylinder has the advantage of returning the piston to a base position. A downside of single acting cylinders is the inconsistent output force through a full stroke due to the opposing spring force. Furthermore, the stroke of a single acting cylinder is limited due to the space taken up by the compressed spring and spring length availabilities. A common maximum stroke of a single acting cylinder is about 80 mm.

How Does Cushioning Work in Pneumatic Cylinders?

The movement of the piston in a pneumatic cylinder can be very fast as the compressed air enters the cylinder. This can create a hard shock when the piston hits the head or end cap. This imposes stress on cylinder components, makes a noise, and transmits vibration to the machine structure. To prevent this, the piston can be decelerated at the vicinity of the caps by cushioning. Cushioning can also prevent the piston from rebounding (bouncing) off the end position.

Why Use Adjustable Cushioning?

In larger cylinders with higher piston speeds or stronger forces, the shock absorption can be achieved by trapping a certain volume of air in the end position. At the end of the stroke the air will be compressed to generate a breaking effect. For this purpose, adjustable flow valves are installed directly on the end ports of the cylinder. This allows the free inflow of pressurized air while allowing the adjustment of the area of the exhaust port with an adjusting screw. This method of cushioning is wear-free and offers optimal cushioning performance. Depending on the operating pressure and the cylinder force, the screw settings on the cylinder need to be adjusted for ideal cushioning. Too much cushioning results in slow strokes and too little cushioning increases the end-of-stroke shock. 

How to Detect a Pneumatic Cylinder's Position?

Most cylinders operate in two positions, extended and retracted. By installing position switches for each case, the control system can be configured to perform the next step after a cylinder reaches a certain point, or to alarm if a cylinder has not reached the position commanded when expected. For this we can use pneumatic valves with a lever on top, that activates when a cylinder pushes on it. It is also possible to add more valves to indicate when actuators reach midway positions, with a special kind of lever as shown in the animation. Another way to detect the position of the cylinder demands that the piston is equipped with a magnet. Body mounted sensors can then receive information from the magnetic field created and therefore recognize the position of the piston in the cylinder.

Pneumatic Cylinder Symbols Explained

The symbol for the pneumatic cylinder often tells us a great deal about the options included and the special features of that particular cylinder. Watch the video to learn more.