Air brakes, mechanical – semi-trailers and trailers.
Semi-trailers and trailers are usually equipped with air brakes, although some trailers still have mechanical brakes.
A trailer equipped with air brakes has its own compressed air storage tank, at which the auxiliary valve of the trailer tank is located. The air tank of the trailer is connected to the tractor brake system by an air line, provided with a connector for connecting the tractor and trailer air hoses. The air hose connecting the tractor to the trailer is constantly under pressure. It is done for this, that in the event of disconnection of the trailer from the towing vehicle (e.g. when driving uphill) rupture of the air line, the air pressure in the line dropped, which will relieve the auxiliary valve of the trailer tank and cause automatic braking of the trailer. A three-way cock in the trailer braking system was installed for this purpose, so that after the trailer breaks off and it brakes automatically, it can be unbraked again.