Air tanks are filled by the emergency supply line from the tractor. Air pressure is sent from the air tanks to the brakes by relay valves. The pressure in the service line tells how much pressure the relay valves should send to the trailer brakes. Do not let water and oil build up in the air tanks. Drain air tanks of water and oil after each working day.
Water can freeze in parts of the brake system making the brakes fail.
Trailer Service, Parking and Emergency Brakes On trailers without spring brakes, the emergency brakes come on whenever the air pressure in the emergency line is lost. These trailers have no parking brake. The emergency brakes will hold only as long as there is air pressure in the trailer air tank. It is important for safety that you use wheel chocks when you park trailers without spring brakes. A major leak in the service line will lower the air tank pressure quickly and cause the trailer emergency brakes to come on.