PULLEY 4S8895 - Caterpillar

Illustration 1 g00862659
Accumulator Charging Valve and Schematic (1) Plug (2) Priority spool (3) Load sensing spool (4) Check valve (5) Fixed restrictor (6) Flow control valve (7) Pressure relief valve (A) Front brake port (B) Inlet port (C) Outlet port (D) Rear brake port (E) Pressure switch portThe brake accumulator charging valve controls the flow of oil from the pump to the brake circuits. The hydraulic oil is diverted, based on the pressure requirements of the brake circuits.When the engine is started, the accumulator charging valve receives the flow of oil from the pilot/brake pump at inlet port (B). Pressure relief valve (7) will cause the pump flow to return to the hydraulic tank if the oil pressure in the brake system is too high.Flow control valve (6) regulates the flow of oil through priority spool (2) to the brake accumulators. When the oil pressure in the incoming line is low, the flow control valve directs the oil to the priority spool through fixed restrictor (5) and check valve (4). The fixed restrictor allows the accumulators to fill at a controlled rate. The check valve prevents the pressure oil in the accumulators from flowing back through the flow control valve. Priority spool (2) is designed to charge either brake accumulator whenever the pressure in the circuit drops to the cut-in pressure.Load sensing spool (3) controls the cut-in and the cut-out pressures for the accumulator charging valve. When the cut-out pressure is reached, the load sensing spool diverts pilot pressure for flow control valve (6) to the hydraulic tank. The control valve will divert the pump flow back to the hydraulic tank through outlet port (C). When this occurs, the accumulators will supply the oil pressure to the brake circuits until the oil pressure drops to cut-in pressure. Check valve (4) will prevent the flow of high pressure oil back through flow control valve. A decrease to cut-in pressure in either brake circuit will cause load sensing spool (3) to shift. This will divert the pump flow into the circuit that is low. This results in a shift of flow control valve (6). When this occurs, the flow control valve will divert the pump flow to the brake accumulators through the inverse shuttle check valve.Pressure switch port (E) connects to the brake oil pressure switch. The brake oil pressure switch sends a signal to the Caterpillar Monitoring System when the brake oil pressure drops below the minimum operating pressure.