Pneumatic control valve for trailer brakes - which holds trailer pressure in direct relationship to towing unit pressure

摘要

The pneumatic brake system of the towing vehicle operates at a high pressure in order to reduce the size of air pressure reservoirs, and to increase the response of braking. The trailer brakes operate at lower pressures and are coupled to the towing unit brakes by a special valve which controls the ratio of pressures rather than the absolute pressure of the trailer brakes. During braking both towing unit and trailer pressures drop by proportionate amounts, while the valve maintains the pressure ratio. This prevents large amounts of air draining from the high pressure side to the low pressure side during successive braking, so that the towing unit brakes remain at their most effective level.