Air suspension, also called pneumatic suspension, uses the properties of air for the cushioning effect (springiness). Air springs are basically pressurized air chambers made up of rubber bellows which maintain constant height under varying loads. The height of the air springs is controlled continuously by adjusting the air pressure in the bellows with the help of a load leveling device connected between the bogie frame and the base plate of air springs. The air springs replace only the secondary suspension, whereas primary suspension continues to use steel coil springs.
An auxiliary air reservoir of 150 litre capacity is provided below each coach, which is fed from feed pipe through a non-return valve. Driver maintains 7 bar pressure in loco compressor and air...
more... springs operate at a limiting pressure of 6 kg/cm².
(Pictures and information curtsy: rcf.indianrailways.gov.in)