The weight of a truck, and thus the axle load, fluctuates greatly depending on the payload at any given moment. To meet the resulting suspension requirements, virtually all commercial vehicle manufacturers now employ air springs. In providing for level control, air springs also guarantee that the vehicle body maintains a constant road clearance. This, in turn, ensures safe driving regardless of the loading conditions. The vehicle body can also be raised or lowered by means of air springs actuated via optional auxiliary manual controls. This is of advantage in adjusting vehicle body height to the level of a ramp or in placing an interchangeable platform.