an air spring is optionally integrated with a shock absorber or other damping unit , and has an air cylinder closed at one end , and in axially - slidable engagement with a sealing head at the other end . a sealed partitioning plate is fixed in the cylinder , and divides the cylinder into a primary air chamber and a secondary air chamber . a sealed air passage connects the primary and secondary air chambers , and can be opened or closed by a simple one - quarter turn rotation of an external knob to instantly switch the air spring between two different spring rate curves .