In vehicles with leaf suspension, an air bellows is mounted between the frame and the rear axle to support the existing leaf springs. The VB-SemiAir is supplied as a two-chamber system, so the air bellows are not connected to each other. 2circuit systems ensure that small charging differences can be compensated for separately on the left and right. The VB-SemiAir is supplied with a drain/fill valve for this purpose. Explanation Single/two-circuit system: Single-circuit system : Both bellows are connected to each other. They are filled via a common line. With the 1-circuit system, only one manometer is required to monitor the entire air pressure in the system. A single-circuit system is only suitable if the wheel loads on the rear axle are identical on both sides and the load on the vehicle is completely uniform. Dual-circuit system: The air bellows on the left and right are both separate and can therefore be filled with different pressures. 2 manometers are required to monitor the pressure. Due to the possibility of varying the pressure separately, load-dependent wheel load differences can easily be compensated for in 2-circuit systems. Inclinations can be compensated.