ENGINE AR-COMPLETE 2444817 - Caterpillar

2-1 Structural Diagram
2-2 Function
This brake valve is mounted on the motor with hexagon socket bolts (15), in a position between the control valve and motor. It consists of the counterbalance valve and relief.(1) Counterbalance valveThe counterbalance valve can be divided into two, the counterbalance spool assembly (24) and the plunger assembly (3). The counterbalance spool assembly consists of the spool and poppet, spring and plug in the spool, and is pushed from both ends by spring (9). (The counterbalance spool assembly cannot be disassembled.)The plunger assembly (3) consists of the plunger, steel ball, spring and spring guide. The counterbalance spool assembly reciprocates in body (1) and automatically regulates the return side from the motor to control motor revolutions proportional to the flow from the control valve, and prevents cavitation in the motor by controlling revolutions. It also prevents abnormal motor running when the motor is turned by an external force. The plunger assembly is coupled to both ends of the counterbalance spool assembly to dampen vibration of the spool assembly. The plunger assembly requires special control and cannot be disassembled.(2) Relief valve assemblyThe relief valve assembly (5) consists of the cartridge and poppet, stem, spring, retainer, set screw, locknut, O-ring and backup ring in the cartridge, and is tightened to body (1) as a cartridge assembly. (This valve is factory adjusted to the rated pressure and must not be disassembled.) The relief valve assembled (5) converts the hydraulic energy into termal energy to limit maximum motor pressure.(3) Parking brake release signalPort G is connected to parking brake chamber of the motor, transmits pilot pressure to control parking brake function of the motor, release parking brake of the motor immediately before starting the motor or operates parking brake right after the motor stops and prevents wild running of the motor by external force. Port G has orifice (11) incorporated.2-3 Operation
(1) Counterbarance valveWhen pressurized oil from the control valve is sent to port A in body (1), it pushes open the poppet in spool (2) and flows into port C in body (1). The oil is then led to the motor from port C and returns from the motor to port D in body (1).Pressure of port A acts on the right surface of counterbalance spool assembly (24) via paths L and M. When this pressure becomes higher than the counterbalance valve operating pressure it overrules spring (9) force and moves the spool assembly to the left.This leads oil to flow to port B from port D via the outer ring groove (throttle K) of spool, goes through control valve and returns to the tank. If oil flows in reverse and enters port B, the reverse operation will be performed.The foregoing operation is when the motor operates nowmally and the brake valve does not make special operation. But when the machine is on a slope traveling downward, the motor rotates by weight of the machine and starts rotating at speed more than the oil supply. In other words wild run