AIR BRAKES -- GENERAL INFORMATIONFigure 17 - Mainifoled Tractor Protection ValveDIFFERENTIAL POWER DIVIDER LOCK VALVEAir can be used to engage or disengage the powerdivider lock used on tandem drive rear axles. Threeconditions are presented to clarify the identification of thepower divider locks.Condition 1Prior to the FMVSS 121 regulation, the air operatedpower divider lock (PDL) had air pressure forengagement (lock) and-spring pressure fordisengagement (released). The air source could be atany convenient location.Condition 2When FMVSS 121 split brake system was introduced,some tandem axles were equipped with power dividerlocks which were disengaged (released) with airpressure and spring controlled in lock or engaged mode.Plumbing of the spring brakes and power divider lock inthis condition eliminated spring brake units at the rearaxle. When the spring brakes are applied, air is expelledfrom the power divider lock allowing the spring pressureto lock up the differential and assist the spring brakes.Figure 18 - 4x2 Tractor With Initial Spilt Air System With Modular Control ValveFor Spring Brake and Tractor Protection ControlCTS-4154Y - Page 16
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