259D Skid Steer Loaders Machine Systems – General Information

Standard Flow

The hydraulic system consists of a hydrostatic drive system, a work tool hydraulic system, and an electrohydraulic system. The hydrostatic drive system and the work tool hydraulic system are controlled by the electrohydraulic system.

The three pumps use one common tank (hydraulic) (10). Pump (Charge) (12) is attached by splines to the pump (implement) (13). Pump (implement) (13) is attached by splines to pump (hydrostatic transmission) (14). Pump (hydrostatic transmission) (14) is attached to the engine by a drive coupling.

Oil from pump (charge) (12) flows to the motor (demand fan) (20) and to the valve (ride control solenoid manifold block) (2), if equipped. Oil flows through the motor (demand fan) (20) to filter (hydraulic oil) (19), to pump (hydrostatic transmission) (14) and valve (travel pilot ON/OFF solenoid) (16). Oil flow continues from pump (hydrostatic transmission) (14) to valve (implement pilot ON/OFF solenoid) (8) and accumulator (hydraulic implements) (9) .

Oil from the pump (implement) (13) flows to the valve (implement) (3). If no hydraulic circuits are active, the oil flows to the tank (hydraulic) (10). This oil is not filtered by the filter (hydraulic oil).

Oil from the pump (hydrostatic transmission) (14) flows to piston motor (hydrostatic) (right side) (17), piston motor (hydrostatic) (left side) (15).

The charge oil moves the swashplates in the piston pumps in order to control piston motors (hydrostatic system).

Oil returns to tank (hydraulic) (10) from the following components: the pump (hydrostatic transmission) (14) , the piston motor (hydrostatic left side) (15), the piston motor (hydrostatic) (right side) (17), pump (implement) (13), valve (implement pilot ON/OFF solenoid) (8), Valve (manual lower for loader arms) (5), valve (implement) (3), oil cooler (10) and valve (ride control solenoid manifold block) (2), if equipped.

High Flow (If Equipped)

The hydraulic system on a machine equipped with high flow capabilities will function the same as a standard flow machine. The high flow machine has been equipped with a two position piston pump (implement) (13) in place of a gear pump.

The machine uses a two position piston pump (implement) (13) to increase to high flow. When the machine ECM receives the correct input from the work tool harness and the auxiliary command (right-hand thumb wheel), the The ECM will send a signal to the high flow solenoid (32). The solenoid (high flow) (32) will allow oil from the cylinder (high flow) (33) to vent to the tank (hydraulic) (10) up stroking the pump.

The machine will provide high flow capabilities when the following conditions are meet:

• A high flow work tool has been detected at the work tool harness.

• The auxiliary command (right-hand thumb wheel) is above 80%.

Hydraulic Supply System

The tank (hydraulic) (10) stores the hydraulic oil for the machine. The hydraulic tank supplies oil to the hydrostatic system, the work tool hydraulic system, and the system for the charge oil.

The gauge - sight (hydraulic tank) (22) is located on the right side of the machine next to the cap (hydraulic tank fill) (21). Maintain the oil level in the green area of the sight gauge. Refer to the Operation and Maintenance Manual, "Hydraulic System Oil Level - Check" for more information.

Sensor (oil temperature) (23) is located on the bottom of the tank (hydraulic) (10). The sensor is a passive sensor with an operating range of 93° ± 1°C (199.4° ± 1.8°F) to 90° ± 1°C (194.0° ± 1.8°F).

Hydraulic oil from the tank (hydraulic) (10) flows into the first section of the pump (implement) (13). The pump (implement) (13) shares a common supply oil with the pump (charge) (12). The gear pumps are driven by a common drive shaft that runs through the pump (hydrostatic transmission) (14). The pump (charge) (12) supplies oil to the hydraulic system and to the hydrostatic system.

Hydraulic oil for the motor (demand fan) (20) is supplied by the pump (charge) (12). Hydraulic oil from the tank (hydraulic) (10) flows to the front section of the pump (implement) (13). The oil flows from the pump (charge) (12) to the motor (demand fan) (20). The flow of oil through the gear motor turns the fan that cools the hydraulic oil that passes through the cooler (11) Tap (24) is the "SOS" tap for the hydraulic system.

The fan motor will rotate in direct relation to the amount of hydraulic oil flow until the hydraulic oil pressure reaches the setting for the relief valve (electrohydraulic proportional) (26). The relief valve (electrohydraulic proportional) allows the excess oil to bypass the gear motor. The relief valve (electrohydraulic proportional) is not a mechanical type of valve. The relief valve (electrohydraulic proportional) is controlled by the ECM based on input by the engine coolant temperature sensor and the hydraulic oil temperature sensor. Use the Caterpillar Electronic Technician software in order to calibrate the demand fan. For more information on the calibration of the demand fan, refer to Hydraulic System Testing and Adjusting, "Gear Motor (fan) - Test".

The check valve (25) allows the gear motor to spin freely after the engine is turned off.

Hydraulic oil then flows out of the motor (demand fan) (20) and into the filter (hydraulic oil) (19). The filter (hydraulic oil) is located in the engine compartment. The filter (hydraulic oil) is a 5 micron filter. The filter (hydraulic oil) removes any particles that could damage the piston pump. From the filter (hydraulic oil), the hydraulic oil flows into the front section of the Pump (hydrostatic transmission) (14).

The filter (hydraulic oil) contains a valve (bypass). Valve (bypass) (28) opens when a differential pressure of 345 kPa (50 psi) is reached. Differential pressure indicator (28) will close when the differential pressure reaches 290 ± 15 kPa (42 ± 2 psi). When the differential pressure indicator closes, an electrical signal causes the light on the right control panel to illuminate. For more information about the alert indicators, refer to the Operation and Maintenance Manual, "Alert Indicators".

Operational Requirements

Certain electrical functions are required before the machine Electronic Control Module (ECM) allows operation of the electrohydraulic controls. The valve (travel pilot ON/OFF solenoid) (16), the electrohydraulic control (hydrostatic system), and the Valve (implement pilot ON/OFF solenoid) (8) are energized under the following conditions:

• The seat must be occupied.

• The left-hand arm bar must be in the DOWN position.

• The parking brake switch must be disengaged.

Note: If the machine is equipped with an optional pattern selector switch, select PATTERN 1 or PATTERN 2 before the parking brake can be released. Refer to Operation and Maintenance Manual, "Operator Controls". Refer to the section on "Selectable Control Pattern and Dedicated Control Pattern".

The valve (implement pilot ON/OFF solenoid) (8) allows the flow of pilot hydraulic oil to the valve (implement) (3). When valve (implement pilot ON/OFF solenoid) (8) is de-energized, no flow of pilot hydraulic oil reaches the control valve (work tool). When the control manifold is energized, pilot hydraulic oil reaches the control valve (work tool).

The valve (travel pilot ON/OFF solenoid) (16) is mounted on the side of the pump (hydrostatic transmission) (14). The solenoid valve allows the flow of hydraulic charge oil to control the actuator spools in the Pump (hydrostatic transmission) (14).

The parking brakes are located on motor (hydrostatic) (left side) (15) and motor (hydrostatic) (right side) (17) piston motor.

When the valve (travel pilot ON/OFF solenoid) (16) is de-energized, the flow of pilot hydraulic oil is blocked. Hydraulic oil from the parking brake actuators drains through the valve (travel pilot ON/OFF solenoid) (16) to the hydraulic tank. The absences of pressurized hydraulic oil will allow the force of the actuator spring to engage the brakes. When the solenoid is energized, hydraulic charge oil flows into the parking brakes. The oil pressure overcomes the force of the spring in order to disengage the parking brakes.

Manual Lowering Valve

The Valve (manual lower, lift arms) (5) is mounted on the fire wall. The Valve (manual lower, lift arms) (5) is an alternate method in order to lower the work tool. Refer to the Operation and Maintenance Manual, "Equipment Lowering with Engine Stopped" for the correct procedure.

System Drain

In order to drain the hydraulic system, a plugged hose is provided near the belly guard of the machine. If the machine is equipped with ride control, split the line in order to drain. Locate the hose assembly and pull the hose assembly through the opening in the belly guard. Remove the plug in order to drain the hydraulic system.