TM 5-3805-261-20PRINCIPLES OF OPERATION.1-29.HYDRAULIC SYSTEM. The hydraulic system is a closed center system. The oil from the variable displacementpump supplies pressure to the parts of the system while the engine is running. The main parts of the system areillustrated and explained in the following paragraphs. Refer to Appendix F for Hydraulic System Schematics.a.HydraulicVariableDisplacementPumpAssemblyandLines(Figure 1-45).Mounted under the cab. Shaftdriven by engine. The variable displacement rear section draws oil from the hydraulic tank and provides oil flow forsteering, articulation, wheel lean, and earthmoving components. The constant displacement front section circulates oil tothe reservoir (tank) through the cooler, the filter, and the strainer.Figure 1-45.b.CombinationValve(Figure 1-46). Located at the left of the variable displacement pump. Oil from thevariable displacement pump flows through the combination valve when the engine is running. It then goes to the controlvalves for the earthmoving components and to the steering metering valve. A hydraulic pressure unloading valve isincluded for cold weather starting.Figure 1-46.1-43
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