HOSE AS 3834293 - Caterpillar

High Speed
When the speed selector switch on the control console is in the HIGH SPEED position, shift valve (5) is energized. In this position, the control piston (9) in each propel motor is open to charge pressure. Each propel motor is at the minimum displacement position. Propel System Operation (531 Machines)
Illustration 2 g00645322
Hydraulic Schematic for the Propel System On the 531 Machines (1) Control piston, (2) Axle propel motor, (3) Return line, (4) Shift valve, (5) Parking brake, (6) Line from fan motor, (7) Line from steering metering pump, (8) Propel charge filter, (9) Charge oil line, (10) Axle propel pump, (11) Manual displacement control valve, (12) Servo valve, (13) Brake interlock valve, (14) Pressure override relief valve, (15) Charge relief valve, (16) Charge check valve, (17) Charge check valve, (18) Forward multifunction valve, (19) Reverse multifunction valve, (20) Flushing valve, (21) Reverse return line, (22) Shift spool, (23) Oil cooler, (24) Hydraulic oil tank, (25) Return manifold and (26) Thermal bypass valve.Parking Brake On Neutral Position
When you run the engine, the propel pump (11) is turning. The secondary oil flow from the fan motor (6) and the steering cylinders (7) provide charge oil for the propel pump. The maximum charge oil pressure in neutral is controlled by the charge relief valve (16) in the propel pump. The charge oil provides makeup oil and charge pressure for the following functions:
propel pump and motor leakage
cooling for the propel pump and motor
charge oil moves the servo piston for the propel pump.
Charge oil releases the parking brakes.
Charge oil shifts the motor displacement for high speed and low speed.In neutral, the manual displacement control valve (12) is in the center position. The charge oil is blocked to the manual displacement control valve. The control lines that go to the pump servo valve are open to the tank. There is equal pressures on both sides of the swashplate. This creates a neutral position. The propel pump will be at zero displacement.When the parking brake is applied the interlock solenoid (14) for the brakes is not energized. In this position, the springs in the parking brake (5) are applied. The charge oil that goes to the manual displacement valve is directed back to the tank. In this condition, the machine will not move even if the propel lever is moved.Low Speed in the Forward Drive Position
Forward movement of the propel control lever mechanically moves the directional control valve (12) that is for the axle propel pump (11). This movement causes charge oil to flow through the bottom of the servo valve (13). The result is an increase in the angle of the swashplate of the propel pump. High pressure oil flows from the propel pump and the oil goes to the propel motor (2). Low pressure oil exits the motor and the oil returns to the propel pump through return line (3). Charge check valve (18) closes when high pressure oil is pumped through the high pressure side of the closed loop. Charge check