A column of gas confined within a container allows it to use the contained pressure to generate force.
In the case of air springs, the gas is air and the container is a sealed fabric-reinforced rubber bellow or sleeve .Similar to a ball inflated with air, the load an air spring will carry depends on its diameter and therefore, the area of the column of air supported and the pressure of air inside it.
Increasing the load an air spring can carry (the force) can be accomplished by increasing the pressure inside the air spring, increasing the diameter of the air spring (and therefore increasing the area) or both. The ability to change the load-carrying capacity simply by changing the air pressure, rather than changing out the spring,is a major advantage air springs have over steel.
Because an air spring consists of a closed volume of air,the compression of the air spring (jounce travel) will cause an increase in pressure,while the extension of the air spring (rebound travel) will cause a decrease in pressure.This allows the air spring to have an automatic tendency to return to the neutral (design) height as it experiences disturbances in the driving surface.The dynamic build-up in compression also helps protect against "bottoming out" .