Drainage of the pneumatic brake control system.
Drain plugs located in the bottoms of compressed air tanks are used to drain the pneumatic brake actuating system. Depending on the size, the motor vehicle can be equipped with one, two or more air tanks, connected to each other in series or in parallel. Usually the pre-tank is of low capacity, so that it can be inflated faster with air. The remaining tanks are filled while driving and supply air to the pre-tank in time, when the air pressure in it drops. The pressure in the tank is checked by means of a pressure gauge in the dashboard of the driver's cabin.
Water and debris collect at the bottom of the air reservoir, which you should every now and then (in accordance with the operating instructions) drain. The drain plug is used to drain the water and debris from the tank, located at the bottom of the tank. Please note, that the drain plug may only be removed from the reservoir, when the compressor is off. The plug should be removed slowly, pressure in the tank to equilibrate with the ambient pressure.