The SX trailer brake system is piped similar to the Schedule X system. Both systems provide air loss safety features. A one-way check valve (9), a third tank (2), a spring brake control valve (19), two four-line two-way check valves (35) and four spring brakes (18) have been added.

 

The addition of spring brakes serves two functions. It provides a method of securing the trailer when parked and acts as an emergency brake for the trailer axle that has lost its supply reservoir pressure. The trailer spring brakes are held off or caged by trailer supply reservoir pressure.

If the trailer has lost all supply reservoir pressure and must be moved, the spring brakes may be released by opening the spring brake control valve (19) located at the rear of the trailer. This directs air from the isolated third tank to release the spring brakes. The spring brakes may be reset by closing the spring brake control valve. Care should be taken when moving the trailer as the service brakes will not apply.

NOTE: Regulation piping diagrams for off highway air brake systems are listed in Appendix I.