The air dryer removes moisture from compressed air in the pneumatic braking system of trucks, trailers and buses. Water in the pneumatic system freezes in valves and lines during winter, causing loss of braking pressure — a direct safety hazard. The dryer cartridge contains desiccant granulate (silica gel or molecular sieve) that adsorbs water vapour from the passing air.
At Filtry.org you will find dryer cartridges for Wabco, Knorr-Bremse, Haldex and Meritor systems fitted in DAF, Iveco, MAN, Mercedes, Renault, Scania and Volvo trucks. We supply HIFI Filter and SF Filter elements in versions with and without oil-coalescence pre-filtration.
The compressor pushes air through the desiccant cartridge. The granulate adsorbs water vapour. When system pressure is reached a regeneration cycle begins — a portion of dry air flows in reverse, desorbing moisture and purging it to atmosphere. The process repeats cyclically.
Every 1-2 years or every 100,000-150,000 km — depending on the vehicle manufacturer and operating conditions. Signs of a spent cartridge include water in the air tanks (visible when draining condensate) or the compressor cycling on more frequently.
Disposable cartridges cannot be regenerated — they are replaced as a unit. Some stationary systems use twin-column regenerative dryers that alternate, but in vehicles the standard is replaceable cartridges.
Saturated desiccant stops adsorbing moisture. Water enters brake valves, actuators and ABS/EBS modules. In winter this causes valve freeze-up and loss of braking. In summer water accelerates internal corrosion of lines and reservoirs.