Abstract: An air brake system for truck and trailer combinations comprises a vehicle load sensing valve in the rear wheel brake line of the truck, a truck-mounted relay valve incorporating a piston or piston assembly responsive to truck braking pressures and adapted to actuate valve means to control delivery of pressure to the seervice brake line, and an additional piston, piston assembly or piston/diaphragm assembly in the relay valve which also actuates the valve means and which is responsive on opposite sides to the input and output pressures respectively of the vehicle load sensing valve.

Abstract: A full-power hydraulic braking system comprises two independently powered service circuits serving separate sets of brakes, a common pedal-actuated dual brake valve controlling operation of said circuits, a spring brake actuator incorporating two hold-off pistons and having a common output to the brakes or brake linkage, and a dual hand control valve for effecting controlled operation of the two sections of the actuator respectively from the two service circuits.

Abstract: A full-power hydraulic braking system comprises two independently-powered service circuits serving separate sets of brakes, a common pedal-actuated dual brake valve controlling operation of said circuits, a spring brake actuator fed from both service circuits through separate lines and, in each of said lines, a pressure responsive protection valve operable in the event of a failure in either service circuit to cut off the spring brake actuator from that service and ensure continued operation of said actuator from the other service circuit.