What is the function of an air dryer in an air brake system?

An AIR DRYER removes MOISTURE (water vapor) and some oil from the compressed air BEFORE it reaches the air storage tanks. CDL air brakes. This reduces water accumulation in the system, which: prevents corrosion and damage; reduces the risk of FREEZING in cold weather (frozen moisture can block valves and cause brake failure); reduces the need for frequent tank draining (though draining is still done). Some systems also use ALCOHOL EVAPORATORS to lower the freezing point of any moisture. Air dryers are common on modern trucks. The air dryer works with the wet tank and tank draining to keep moisture out of the brake system. Knowing the air dryer's function (removing moisture/oil to prevent water buildup and freezing) is commonly tested.