Dampness in the compressed-air braking system is extremely dangerous, because the water can freeze in winter and/or disturb the
function of the brake, e.g., through corrosion. The air tanks of the first compressed-air brake systems had to be drained regularly. This was possible by either hand-operated or automatic drainage valves. Additionally, there was earlier also an anti-freeze pump which had to be refilled regularly. In this respect, the air dryer is an effective helper. Instead of removing the dampness from the system later, it is more favorable not to let it in at all. By taking several measures, the intake air becomes, as a rule, so dry, that even when it is really cooled, it no longer gives off any dampness.
The air coming from the compressor is first cooled down in a long, slightly winding tube, in the pressure control valve and then in the air dryer, thus already losing dampness through condensation. In the air dryer, it is then conducted through a drying agent. The higher the pressure, and the lower the temperature, the more steam the drying agent can absorb. After reaching the switch-off pressure, (in the pressure control valve) a small amount of the compressed-air, stored in a separate, small air tank is directed, under low pressure, back through the drying agent and then released into the open, whereby, it absorbs dampness and regenerates it. 10/09