Grades 6–8 · Machines
How does compressed air push a cylinder rod?
A pneumatic cylinder uses compressed air to move a piston and its attached rod. Pneumatic means powered by a gas, usually air. The piston fits inside a cylinder so that different pressures can act on its two faces.
In the diagramCompressed air pushes a fitted pistonPressurized sideVented side200 kPa gaugePiston area 2 cm²Ideal extension force: 40 N
For extension in this illustration, compressed air acts on the full piston face while the opposite chamber is vented to the atmosphere. The relevant input is gauge pressure: pressure above the atmospheric reference. It is this difference, not absolute pressure alone, that provides the modeled net push.
Ideal force equals pressure difference multiplied by piston area. A gauge pressure of 200 kilopascals acting on 2 square centimeters gives 40 newtons. Doubling area at the same pressure gives 80 newtons, while zero gauge pressure produces no net pneumatic extension force under these assumptions.
Compressed air can change volume and store energy, so a complete motion calculation would also need flow and changing pressure. This diagram isolates force at stated conditions. Real cylinders lose some force to friction, and retracting a rod can involve a smaller effective area. The calculated force does not specify speed, air use or a safe carried load.
About this explanation
Starting knowledge: Understand pressure as force per area and convert simple square-centimeter quantities.
Sources
- Festo — Cylinder Sizing by Piston Force