- Load Haul Dump:
- R2900G (S/N: JLK865-UP)
The hydraulic schematic for the service and parking brake system has incorrect information. Replace the information with the following information.
Service and Parking Brake System
S/N: JLK865-UP
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| Illustration 1 | g01507754 |
Hydraulic schematic for the braking system (1) Brake release cylinder (2) Pressure tap for the brake release system (3) Brake release sequence valve (4) Connection for the brake release system (5) Parking brake control valve (6) Shuttle valve (7) Shuttle valve (8) Front wheel brakes (9) Parking brake oil pressure switch (10) Pressure tap for the park brake circuit (11) Line to pilot circuit (12) Brake accumulator oil pressure switch - alert indicator (13) Brake accumulator oil pressure switch - brake application (14) Brake accumulator (15) Service brake and transmission neutralizer pedal (16) Service brake pedal (17) Check valve (18) Check valve (19) Residual brake oil pressure switch (20) Service brake oil pressure switch (21) Brake accumulator relief valve (22) Portable hydraulic pump quick connect coupler (23) Pressure tap for the brake accumulator circuit (24) Service brake control valve (25) Brake accumulator charging valve (26) Pilot relief valve (27) Pressure tap for pilot system (28) Pilot oil filter (29) Check valve (30) Portable hydraulic pump quick connect coupler (31) Pilot and braking pump (32) Hydraulic tank (33) Breaker relief valve (34) Rear wheel brakes | |
Wheel brakes (8) and (34) are divided into two sections. The service brake section is an oil pressure applied and spring released brake. The parking brake section is an oil pressure disengaged and spring engaged brake. The service brake can be used when the parking brake is disengaged.
The service brakes are controlled by two brake pedals in the operator station. The left and right brake pedal assemblies are connected by a mechanical linkage. The left pedal is service brake and transmission neutralizer pedal (15). The right pedal is service brake pedal (16) .
When service brake pedal (16) is depressed, only the service brakes are applied. When service brake and transmission neutralizer pedal (15) is depressed, the service brakes are applied and the transmission is neutralized. This allows the full engine power to be used in the hydraulic system. When service brake and transmission neutralizer pedal (15) is released, the transmission engages and the service brakes are released.
With the engine running, oil flows from hydraulic tank (32) to pilot and braking pump (31) which is part of the steering, pilot and braking pump. The oil then flows from pilot and braking pump (31) through check valve (29) to brake accumulator charging valve (25) .
The piston in brake accumulator (14) is held against the oil intake end with dry nitrogen gas. Brake accumulator (14) stores hydraulic oil pressure for the service brakes.
After the service brakes have been activated several times, the volume of oil in the accumulator is less. When the pressure in the brake accumulator decreases, brake accumulator charging valve (25) routes oil from pilot and braking pump (31) to brake accumulator (14). When the brake accumulator oil pressure rises, the charging spool in brake accumulator charging valve (25) blocks the flow of oil to brake accumulator (14) and routes the flow of oil to the pilot circuit.
From brake accumulator (14), the oil flows to service brake control valve (24). Service brake control valve (24) is a tandem valve that routes brake oil to both the front axle service brakes and the rear axle service brakes.
When a brake pedal is depressed, oil flows through service brake control valve (24) where pressure to the service brakes is reduced. Oil flows out of the top port to rear wheel brakes (34), and out of the bottom port to front wheel brakes (8). Oil pressure is higher for the rear service brakes than that of the front service brakes.
Oil pressure flows into the service brake section of the wheel brakes and acts against the service brake piston, causing the machine to slow down or stop.
The parking brake is controlled by a switch on the dash panel in the operator station. The parking brake will not disengage until the engine is running and the service brake oil pressure reaches operating pressure. The parking brake will automatically engage if brake system oil pressure drops below the operating range. When the parking brake control switch is moved to the ON position, all parking brakes are engaged.
With the engine running, oil flows from pilot and braking pump (31) through brake accumulator charging valve (25) to pilot oil filter (28). Oil flows from pilot oil filter (28) to pilot relief valve (26). Pilot relief valve (26) maintains a constant pressure in the pilot circuit. Pilot oil flows from pilot relief valve (26) to parking brake control valve (5) .
When the parking brake switch in the operator station is moved to the OFF position, the solenoids of parking brake control valve (5) are energized. Oil flows through parking brake control valve (5) to both axles. Oil pressure then disengages the parking brake in each wheel brake assembly.
The parking brake control valve solenoids are de-energized when the parking brake switch is moved to the ON position, or the engine start switch key is turned to the OFF position. This will cause parking brake control valve (5) to return the parking brake oil to hydraulic tank (32). The parking brake is now engaged.
If the parking brake is engaged due to a machine fault and the machine must be towed, the machine parking brake can be released manually.
ReferenceFor information on manually releasing the parking brake, refer to Systems Operation, Testing and Adjusting, "Parking Brake - Manual Release" for the machine that is being serviced.
Certain Caterpillar machines equipped with the optional remote control system may be equipped with the optional brake release system. If the parking brake is engaged due to a machine fault and the machine must be towed, the brake release system can be used to release the machine parking brakes.
ReferenceFor information on the brake release system, refer to Systems Operation, Testing and Adjusting, "Brake Release System".