259D Skid Steer Loaders Machine Systems – Work Tool Hydraulic System

High Flow (If Equipped)

The piston pump for the hydrostatic system is mounted to the engine. The piston pump (6) for the work tools is mounted to the piston pump for the hydrostatic system. Piston pump (6) supplies the work tool hydraulic system with oil. When the engine speed increases, the speed of piston pump (work tool) (6) increases. The increased speed of the pump will move oil to the work tool hydraulic system. Control valve (work tool) (7) is a closed center control valve.

The pilot oil for the work tool hydraulic system is supplied by the gear pump (charge oil) (5). The gear pump (5) is splined to the drive shaft of the piston pump (6). Oil flows out of pump (5) to the fan drive motor. The oil flows through the fan drive motor to the oil filter. From the oil filter, the oil flows to the piston pump for the hydrostatic system. At the piston pump, the hydraulic oil flows passed the relief valve (charge) (12) and the valve (travel pilot ON/OFF solenoid) (13). Charge oil exits the hydrostatic piston pump and flows to the valve (implement pilot ON/OFF solenoid) (10). In order for the oil to flow to control valve (work tool) (7), all three of the electronic interlocks must be disengaged. In order for oil to flow through the (implement pilot ON/OFF solenoid) (10), the hydraulic enable solenoid must be energized.

When the engine starts rotating, charge oil will supply the hydraulic accumulator (11). The gear pump (charge oil) directs oil flow to the valve (implement pilot ON/OFF solenoid) (10). The oil flows downstream across a one-way flow check valve. The oil will flow directly to the hydraulic accumulator (11). Oil will flow to the hydraulic accumulator (11) without having electrical components energized. The charge oil flows to the valve (implement pilot ON/OFF solenoid) (10). When valve (implement pilot ON/OFF solenoid) (10) is activated, oil will be directed to control valve (work tool) (7). The electrohydraulic control lever for the hydraulic work tool must be activated to a desired position in order to activate the solenoid valve. Once the solenoid valve is activated the pilot oil shifts the control spool to the desired position. Once any control spool shifts, high-pressure oil from the piston pump (work tool) (6) will flow to the selected circuit. Relief valve (charge) (12) maintains the pressure for the charge oil.

Hydraulic System for the Lift Cylinders

When the control lever for the work tool is moved to the RAISE position, the RAISE solenoid on the control valve (work tool) (7) is activated. The solenoid valve allows pilot oil to flow to the left side of the lift spool that is part of the control valve (work tool) (7). The pilot oil causes the lift spool to shift to the right.

Hydraulic oil flows from the piston pump (work tool) (6) into the control valve (work tool) (7). The oil then flows past the lift spool and into the line for the head end of the lift cylinder (4)

As oil forces the rods of the lift cylinders to extend, oil is forced out of the rod end of the cylinders. The oil that flows from the rod ends of the cylinders flows to the lift spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

When the electrohydraulic control lever for the work tool is moved to the LOWER position, pilot oil flows to the right side of the lift spool that is part of control valve (work tool) (7). The pilot oil causes the lift spool to shift to the left. Hydraulic oil flows from piston pump (work tool) (6) through the spool and into the line for the rod end of the lift cylinder.

As oil forces the rods of the lift cylinder to extend, oil is forced out of the rod end of the cylinders. The oil that flows from the rod ends of the cylinders flows to the lift spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

The FLOAT position allows the work tool to follow the contour of the ground. The FLOAT position is activated by moving the joystick to the LOWER position and pressing the trigger.

Once the FLOAT function is engaged, the trigger can be released. The joystick can then be returned to the NEUTRAL position without affecting the float function. FLOAT will remain engaged until the trigger on the right-hand joystick is pressed again. The float function will disengage also when the bucket is raised or when the bucket is lowered.

When the control lever for the work tool is moved to the FLOAT position, the LOWER solenoid valve is activated. The solenoid valve allows pilot oil to flow to the right side of the lift spool that is part of the control valve (work tool) (7). The pilot oil causes the lift spool to shift fully to the left. With the spool shifted, the spool opens the rod ends and the head ends of the lift cylinders to the hydraulic oil tank (3). The weight of the work tool will cause the work tool to lower to the ground. The work tool will then follow the contour of the ground. Supply oil from the piston pump (6) will continue to flow to control valve (work tool) (7). Supply oil will not flow to the lift cylinder (4). The tilt spool may be operated when the lift spool is in the FLOAT position.

In the event of engine failure, the manual lowering valve (8) is used to lower the lift arms manually. The manual lowering valve (8) allows oil to drain out of the head end of the lift cylinders. The hydraulic oil flow is directed to the Hydraulic oil tank.

Hydraulic System for the Tilt Cylinders

The hydraulic oil is directed to the tilt spool in the control valve (work tool) (7) by the DUMP and RACK solenoid valves. The end of the spool that receives the pilot oil depends on the position of the electrohydraulic control lever for the work tool.

As the spool is shifted, hydraulic oil from the piston pump (6) flows through the tilt spool and into the tilt cylinders (2). Oil that leaves the tilt cylinders flows to the tilt spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

Auxiliary Hydraulic System (High Flow)

Note: Refer to Illustration 1 and Illustration 2 for reference to callouts.

When thumb wheel (29) is moved, pilot oil is directed to the auxiliary circuit spool (14) that is located in the control valve (7). Thumb wheel (29) is a proportional switch. Move the thumb wheel slightly for a small amount of flow to the auxiliary couplings. Move the thumb wheel farther in order to obtain a higher flow to the auxiliary couplings. When a high flow work tool is detected by the ECM at the work tool electrical connector, movement of the thumbwheel beyond 80% of the switch travel range will trigger the high flow mode giving maximum flow. Refer to "High Flow Mode" in this manual.

Move the thumb wheel backward in order to increase the flow of oil to the female "Aux 1" coupling (25). When you move the thumb wheel (29) backward, the ECM activates solenoid (16). Pilot oil from gear pump (charge oil) (5) moves through the energized solenoid in order to activate the spool (14). Supply oil from the piston pump (work tool) (6) flows through the spool (14) to the female "Aux 1" coupling (25). Oil from the piston pump flows through the work tool circuit. Then the oil flows back through the male "Aux 2" coupling (26) to the spool for the auxiliary (14). The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

Move the thumb wheel forward in order to increase the flow of oil to the male "Aux 2" coupling (26). When you move the thumb wheel (29) forward, the ECM activates solenoid (24). Pilot oil from gear pump (charge oil) (5) moves through the energized solenoid in order to activate the spool (14). Supply oil from the piston pump (work tool) (6) flows through the spool (14) to the male "Aux 2" coupling (26). Oil from the piston pump flows through the work tool circuit and back through the female "Aux 1" coupling (25). The oil then flows to the spool for the auxiliary (14). The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

High Flow Mode

The ECM must detect the presence of a high flow work tool through the electrical connection on the loader arm in order to activate high flow mode. The ECM must also detect a position of the auxiliary thumbwheel (29) beyond 80% of the travel range in order to activate high flow mode. Under these conditions, the ECM will send an electrical signal to the pump control solenoid mounted on the two position piston pump (work tool) (6), which will shift the position of the swashplate from the standard flow angle to the high flow angle, effectively increasing the pump displacement.

Note: High flow mode required an electrical connection that is located on the loader arm. Refer to Operation and Maintenance Manual, "Work Tool Operation" for additional information.

Standard Flow

The piston pump for the hydrostatic system is mounted to the engine. The gear pump (6) for the work tools is mounted to the piston pump for the hydrostatic system. Gear pump (6) supplies the work tool hydraulic system with oil. When the engine speed increases, the speed of gear pump (work tool) (6) increases. The increased speed of the pump will move oil to the work tool hydraulic system. Control valve (work tool) (7) is an open center control valve.

The pilot oil for the work tool hydraulic system is supplied by the gear pump (charge oil) (5). The gear pump (charge oil) (5) is splined to the drive shaft of the gear pump (work tool) (6). Oil flows out of the gear pump (charge oil) (5) to the fan drive motor. The oil flows through the fan drive motor to the oil filter. From the oil filter, the oil flows to the piston pump for the hydrostatic system. At the piston pump, the hydraulic oil flows past the relief valve (charge) (12) and the valve (travel pilot ON/OFF solenoid) (13). Charge oil exits the hydrostatic piston pump and flows to the valve (implement pilot ON/OFF solenoid) (10). In order for the oil to flow to the control valve (work tool) (7), all three of the electronic interlocks must be disengaged. In order for oil to flow through the valve (implement pilot ON/OFF solenoid) (10), the hydraulic enable solenoid must be energized.

When the engine starts rotating, charge oil will supply the accumulator (11). The charge pump directs oil flow to the valve (implement pilot ON/OFF solenoid) (10). The oil flows downstream across a one-way flow check valve. The oil will flow directly to the accumulator (11). Oil will flow to the accumulator (11) with no electrical components energized. The charge oil will also flow to the valve (implement pilot ON/OFF solenoid) (10). When the valve (implement pilot ON/OFF solenoid) (10) is activated, oil will be directed to the control valve (work tool) (7). The electrohydraulic control lever for the hydraulic work tool must be activated to a desired position in order to activate the solenoid valve. Once the solenoid valve is activated the charge oil shifts the control spool to the desired position. Once any control spools shift, the high-pressure oil from the gear pump (work tool) (6) will flow to the selected circuit. Relief valve (charge) (12) maintains the pressure for the charge oil.

Hydraulic System for the Lift Cylinders

When the control lever for the work tool is moved to the RAISE position, the RAISE solenoid on the control valve (work tool) (7) is activated. The solenoid valve allows pilot oil to flow to the left side of the lift spool that is part of the control valve (work tool) (7). The pilot oil causes the lift spool to shift to the right.

Hydraulic oil flows from the gear pump (work tool) (6) into the control valve (work tool) (7). The oil then flows past the lift spool and into the line for the head end of the lift cylinder (4) .

As oil forces the rods of the lift cylinder to extend, oil is forced out of the rod end of the cylinders. The oil that flows from the rod ends of the cylinders flows to the lift spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

When the control lever for the work tool is moved to the LOWER position, the pilot oil flows to the right side of the lift spool in the control valve (work tool) (7). The pilot oil causes the lift spool to shift to the left. Hydraulic oil flows from the gear pump (work tool) (5) through the spool and into the line for the rod end of the lift cylinders.

As oil forces the rods to retract, the oil is forced out of the head end of the cylinders. The oil flows to the lift spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

The FLOAT position allows the work tool to follow the contour of the ground. The FLOAT position is activated by moving the joystick to the LOWER position and pressing the trigger.

Once the FLOAT function is engaged, the trigger can be released. The joystick can then be returned to the NEUTRAL position without affecting the float function. FLOAT will remain engaged until the trigger on the right-hand joystick is pressed again. The float function will disengage also when the bucket is raised or when the bucket is lowered.

When the control lever for the work tool is moved to the FLOAT position, the LOWER solenoid valve is activated. The solenoid valve allows pilot oil to flow to the right side of the lift spool that is part of the control valve (work tool) (7). The pilot oil causes the lift spool to shift fully to the left. With the spool shifted, the spool opens the rod ends and the head ends of the lift cylinders to the hydraulic oil tank (3). The weight of the work tool will cause the work tool to lower to the ground. The work tool will then follow the contour of the ground. Supply oil from the gear pump (6) will continue to flow to control valve (work tool) (7). Supply oil will not flow to the lift cylinder (4). The tilt spool may be operated when the lift spool is in the FLOAT position.

In the event of engine failure, the manual lowering valve (8) is used to lower the lift arms manually. The manual lowering valve (8) allows oil to drain out of the head end of the lift cylinders. The hydraulic oil flow is directed to the Hydraulic oil tank.

Hydraulic System for the Tilt Cylinders

The hydraulic oil is directed to the tilt spool in the control valve (work tool) (7) by the DUMP and RACK solenoid valves. The end of the spool that receives the pilot oil depends on the position of the electrohydraulic control lever for the work tool.

As the spool is shifted, hydraulic oil from the gear pump (6) flows through the tilt spool and into the tilt cylinders (2). Oil that leaves the tilt cylinders flows to the tilt spool. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (3) .

Auxiliary Hydraulic System (Standard Flow)

When you activate any of the auxiliary hydraulic controls (14), (15), (17), or (18) that are located on the joystick control (16), pilot oil is directed to the auxiliary circuit spool. The auxiliary circuit spool is located in the control valve (work tool) (7).

When the auxiliary hydraulic control (17) is activated, the Electronic Control Module (ECM) activates the auxiliary hydraulic solenoid. Pilot oil from the gear pump (charge oil) (5) moves through the energized solenoid in order to activate the auxiliary hydraulic spool. The pilot oil causes the auxiliary spool to shift to the left. Supply oil from the gear pump (work tool) (7) flows through the spool to the coupling (1). Oil from the gear pump flows through the work tool circuit and back through the coupling (1) to the spool for the auxiliary. The oil then flows out of the control valve (work tool) (7) and back to the hydraulic oil tank (5) .

For more information on the operation of the hydraulic system for the auxiliary, refer to the Systems Operation, "Control Valve (Work Tool)".