259D Skid Steer Loaders Machine Systems – Control Valve (Work Tool)

Standard Flow

Note: All references to the joystick control are based on the standard Caterpillar Joystick Control Pattern. Refer to Operation and Maintenance Manual , "Operator Controls". Refer to the section on "Selectable Control Pattern and Dedicated Control Pattern".

The control valve (work tool) (1) is an electrohydraulic controlled, open center valve . Any movement of the right-hand joystick (24) will send a Pulse Width Modulation Signal signal (PWM) to the machine Electronic Control Module (ECM). The machine ECM will regulate electrical current to the corresponding solenoid in order to regulate pilot oil to the control valve spool.

If the right-hand joystick (24) is not moved, oil flows into inlet (9) . From inlet (9) oil flows past each of the spools and out of the outlet (8) to the tank. No movement of the implements occurs.

The control valve (work tool) (1) contains three control valve spools. Valve spool (26) controls the lift cylinder functions. Lift cylinder control spool (26) is controlled by solenoid valves (4) and (14) . Valve spool (22) controls the tilt cylinder functions. The tilt cylinder control spool (22) is controlled by solenoid valves (3) and (15) . Valve spool (27) controls the auxiliary functions. The auxiliary control spool (27) is controlled by solenoid valves (2) and (16) .

The control valve (work tool) (1) contains a main relief valve and four line relief valves. The main relief valve (53) limits the maximum system pressure in the work tool hydraulic system. The line relief valves limit the maximum hydraulic pressure in the individual lines.

The return oil from the "A" port (29) on the tilt function is in series with the central supply passage (21) . When the operator moves the joystick to the dump position oil from the tilt cylinder returns through "A" port (29) . The flow is directed back into the series passage and is available to the lift function and the auxiliary function. Return oil from "B" port (30) is directed to the tank.

Each function of the control valve contains a load check valve. The load check valve is used in order to prevent the oil from the cylinder back-flowing into the series passage. When the system pressure increases above the pressure in the work tool circuit, the load check valve opens allowing system oil to flow to the work tool.

High Flow (If Equipped)

The functionality of the valve will remain the same when the machine is in high flow mode. Machines with High Flow capabilities will be equipped with a two position piston pump that has a swash plate controlled by a solenoid. The solenoid will receive a signal and up stroke the pump when the ECM sees the following conditions;

• The machine detects a high flow auxiliary work tool present.

• The thumb wheel is at or above 80%.

Lift Control Section

HOLD Position

When the right-hand joystick (24) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet (9) to the lift control spool (26) through the central supply passage (21) . Refer to Operation and Maintenance Manual, "Operator Controls " for lift control of the right-hand joystick.

The spool blocks the oil from entering any of the passages. Oil cannot flow to port "A" (29) or port "B" (30) . The spring (28) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the lift cylinders occurs.

Oil in passage (21) will flow into the central return passage (17) . The oil then flows through the outlet (8) to the hydraulic tank.

RAISE Position

When the right-hand joystick (24) is moved to the RAISE position, the right-hand joystick (24) will send a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the raise solenoid (4) on the control valve (work tool) (1) . The raise solenoid (4) will direct pilot oil to the right end of the lift cylinder control spool (26) . The pilot oil (32) forces the spool (26) to move to the left against the force of the spring (28) . Refer to Operation and Maintenance Manual, "Operator Controls " for RAISE position of the right-hand joystick.

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (7) for the lift circuit and flows through the bridge passage (33) and around the spool to port "A" (29) . From port "A" (29) , oil flows to the head ends of the lift cylinders in order to raise the lift arms.

Return oil from the rod ends of lift cylinders flows into port "B" (30) , and through the tank passage (17) to outlet (8) .

When the right-hand joystick (24) is released from the RAISE position, the spring (28) shifts the spool back to the HOLD position.

LOWER Position

When the right-hand joystick (24) is moved to the LOWER position, the right-hand joystick (24) will send a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the lower solenoid (14) on the control valve (work tool) (1) . The lower solenoid (14) will direct pilot oil to the left end of the Lift Cylinder Control Spool (26) . The pilot oil (34) forces the spool to move to the right against the force of the spring (28) . Refer to Operation and Maintenance Manual, "Operator Controls " for LOWER position of the right-hand joystick.

Oil is blocked from the inlet (9) by the spool. The oil opens the check valve (7) for the lift circuit and flows through the passage (33) and around the spool to port "B" (30) . From port "B" (30) , oil flows to the rod ends of the lift cylinders in order to lower the lift arms.

Return oil from the head ends of the lift cylinders flows into port "a" (29) . The oil flows through the tank passage (147) into outlet passage (8) .

When the right-hand joystick (24) is released from the LOWER position, the spring (28) shifts the spool back to the HOLD position.

FLOAT Position

When the FLOAT function has been activated, the right-hand joystick (24) will send a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the lower solenoid (14) on the control valve (work tool) (1) . The lower solenoid (14) will direct pilot oil to the left end of the Lift Cylinder Control Spool (26) . The pilot oil (34) forces the spool to move to the right against the force of the spring (28) and . Refer to Operation and Maintenance Manual, "Operator Controls " for FLOAT position of the right-hand joystick.

Oil continues to flow from the inlet (9) through the central passage (21) . If the tilt control spool and the auxiliary control spool are in the HOLD position, oil in passage (21) will flow into the central return passage (17) . The oil then flows through the outlet (8) to the hydraulic tank.

Oil that is in the rod ends of the lift cylinders can flow to the tank through port "B" (30) . Oil that is in the head ends of the lift cylinders can flow through port "A" (29) and to tank passage (17) . The work tool will lower to the ground and the work tool will follow along the contour of the ground.

The Lift Cylinder Control Spool (26) will remain in the FLOAT position until the operator moves the right-hand joystick (24) . When the right-hand joystick (24) is released from the FLOAT position, the spring (28) shifts the spool back to the HOLD position.

Tilt Control Section

HOLD Position

When the right-hand joystick (24) is in the HOLD position, no PWM signal is sent to the machine ECM. Oil flows through the inlet (9) , around the lift control spool (26) , and to the tilt control spool (22) through the central supply passage (21) . From the tilt control spool, the oil flows around the auxiliary circuit spool (27) into the central return passage (17) . The oil then flows through the outlet (8) to the hydraulic tank. Refer to Operation and Maintenance Manual, "Operator Controls " for tilt control of the right-hand joystick.

The spools block the oil from entering any of the passages. Oil cannot flow to port "A" (20) or port "B" (18) . The spring (40) keeps the spool centered because the pilot oil is not flowing to the spool. No movement in the tilt cylinders occurs.

TILT DUMP Position

When the right-hand joystick (24) is moved to the TILT FORWARD position, the right-hand joystick (24) will send a PWM signal to the machine ECM. The machine ECM will regulate an electrical current to the tilt forward solenoid (15) on the control valve (work tool) (1) . The tilt forward solenoid (15) will direct pilot oil to the left end of the tilt cylinder control spool (22) . The pilot oil (44) forces the spool (22) to move to the right against the force of the spring (40) . Refer to Operation and Maintenance Manual, "Operator Controls " for TILT FORWARD position of the right-hand joystick.

Oil flows from the inlet (9) to the tilt control spool (22) through the central supply passage (21) . Oil is blocked from the inlet (9) by the spool (22) . The oil opens the check valve (6) for the tilt circuit and flows through the bridge passage (19) and around the spool to port "B" (18) . From port "B" (18) , oil flows to the head ends of the tilt cylinders in order to tilt the work tool forward.

Oil that is returning from the rod ends of tilt cylinders flows into port "A" (20) . The oil flows through the tilt spool (22) and into the central supply passage (21) . The oil can either be used by the lift function or the auxiliary function or flow into the central return passage (17) and to the outlet (8) .

When the right-hand joystick (24) is released from the TILT FORWARD position, the spring (40) shifts the spool back to the HOLD position.