The field of the invention pertains to truck trailers having air ride suspension systems and in particular to air ride tandem truck trailers incorporating means to elevate or lower the rear end of the bed of the truck trailer so as to meet a loading dock or other platform adjacent to the bed of the trailer.
The typical tandem axle air ride trailer suspension comprises four air ride bags which act as fluid springs supporting the bed of the trailer. An air bag is adjacent to each of the four wheel sets of the tandem suspension. On each side of the tandem suspension the two air bags are in fluid communication with a leveling valve having mechanical means to sense the lateral tilt of the trailer bed with respect to the tandem axles. The leveling valves in turn are in communication with a source of pressurized air which completes the air ride system. Typically, the source of air pressure is the air brake system including the air brake reservoir of the truck and trailer combination. To prevent failure of the air ride circuitry from affecting the air brake system of the truck trailer combination, a brake protection valve is inserted in the circuit between the air brake rservoir and the air ride suspension fluid circuitry.
In addition to the air ride fluid circuitry, the brake system for the tandem trailer includes fluid circuitry leading to each spring brake chamber for each of the wheel sets. To release the spring brakes or parking brakes, the fluid circuitry leading thereto is pressurized from the air brake system of the truck trailer combination.