This 3543010-K0200 air dryer assembly (air processing unit with four-circuit protection valve) is a core pneumatic component of Dongfeng heavy truck air brake system. It removes moisture and oil impurities from compressed air generated by air compressor, protects brake valves, air chambers and other pneumatic parts from rust and icing, ensuring stable and reliable air supply for drum brake system. The integrated structure combines drying cylinder and four-circuit protection valve. The shell adopts high-strength alloy casting, anti-corrosion and pressure-resistant. Desiccant inside efficiently absorbs water vapor. Every air dryer assembly undergoes air tightness and functional test before delivery. It is an essential replacement spare part for heavy truck chassis brake pneumatic system maintenance.