The Basic Principles of Air Springs

There are two basic types of air springs used in vehicle suspensions: reversible sleeve and convoluted. Regardless of whether an air spring is a reversible sleeve or convoluted style it will operate on the same principle; when a volume of gas confined within a container is compressed, it produces a reaction force... In the case of air springs the gas is air and the container is a sealed fabric-reinforced rubber bellows 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.

The two basic relationships used in determining the load carrying capability of an air spring are:
(1) From the relationships above, it can be seen that increasing the load an air spring can carry, 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 air spring is a major advantage that air springs have over steel springs. 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, or design, height it is set to ride at as it experiences disturbances in the driving surface. 

The dynamic build-up in compression also helps protect against “bottoming out” and can be further increased on the reversible sleeve air spring by the addition of a “flare” at the bottom of the piston.

(1) From the relationships above, it can be seen that increasing the load an air spring can carry, 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 air spring is a major advantage that air springs have over steel springs. Because an air spring consists of a closed volume of air, the compression of the air spring.