In brief
A pneumatic cylinder converts the energy of compressed air into linear motion and serves as an actuator in automation and mechanical engineering.
Contents
What is Pneumatic cylinder?
Inside the cylinder barrel, compressed air moves a piston whose piston rod transmits the force to the outside. In single-acting cylinders, compressed air works in only one direction and a spring provides the return stroke. Double-acting cylinders are pressurised with compressed air in both directions. There are also special designs such as rodless cylinders, compact cylinders, guided cylinders and rotary actuators.
Key parameters are piston diameter, stroke, operating pressure, cushioning and port thread; together they determine force and speed. For common designs, standards specify the mounting dimensions, for example ISO 15552 for standard cylinders, ISO 6432 for small-bore round cylinders and ISO 21287 for compact cylinders. As a result, cylinders from different manufacturers are often mechanically interchangeable, even if details such as sensor slots or cushioning differ.
Wear parts are mainly piston and rod seals as well as guide bands, which can be replaced as seal kits. End-position cushioning and sensing of the piston position are important features.
In practice: maintenance and procurement
For replacement, the design, piston diameter, stroke, mounting and sensors are required. With standard cylinders, it is worth checking whether a part from another manufacturer with the same mounting dimensions is available more quickly.
Synonyms and abbreviations: air cylinder · pneumatic actuator · compressed air cylinder · pneumatic ram
Frequently asked questions
How do you calculate the force of a pneumatic cylinder?
The theoretical force is pressure multiplied by piston area. A cylinder with a 50 mm piston diameter has an area of around 1,963 mm²; at 6 bar, i.e. 0.6 N/mm², this gives approximately 1,180 N on extension. Friction losses reduce this value. On retraction the force is smaller, because the piston rod occupies part of the area.
When is it worth replacing the seals rather than the whole cylinder?
A seal kit makes sense if the cylinder barrel and piston rod are undamaged and only leaks or declining force occur. If the piston rod shows scoring, corrosion or bending, replacing the cylinder is usually the better choice. For small standard cylinders, a new part is often more economical; for large or custom-made cylinders, repair is more likely to pay off.
What does end-position cushioning do?
End-position cushioning slows the piston down shortly before it reaches the end position so that it does not strike hard. Elastic cushioning works with buffers made of plastic or elastomer, pneumatic cushioning with a trapped air cushion that can often be adjusted via a throttle screw. A suitable setting protects the cylinder, mountings and moving parts and reduces noise.