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| Illustration 1 | g01060664 |
Standard Hydraulic Schematic (1) Steering cylinder (2A) Metering Pump for the 908 (2B) Metering Pump for the 906 (3) Coupler cylinders (4) Auxiliary couplings (5) Tilt cylinder (6) Lift cylinder (7) Bank valve (8) Solenoid valve ( coupler) (9) Piston pump ( hydrostatic) (10) Gear pump (11) Fan drive motor (12) Hydraulic tank (13) Cooler bypass valve ( low pressure) (14) Cooler bypass valve ( high pressure) (15) Cooler (16) Accumulator (17) Solenoid valve ( pilot shutoff) (18) Pilot valve for the auxiliary (19) Pilot valve for the implements (A) Hystat charge oil and pilot supply oil (B) Hystat supply for REVERSE (C) Hystat supply for FORWARD (D) Return oil from the master cylinder (E) Return line from the motor case (F) Return line from the pump case (G) Supply oil to the bearing for the piston motor | |
The work tool hydraulic system is supplied by the gear pump (10). The gear pump provides oil to the following components through the bank valve (7) : metering pump (2), auxiliary couplings (4), tilt cylinder (5) and lift cylinder (6). The pilot valves (18) and (19) provide pilot oil from the charge pump on the piston pump (9) to the bank valve in order to move the spools in each control valve.
The fan motor (11) and the coupler cylinders (3) are also supplied by the gear pump.
Return oil from the work tool flows back into the bank valve, through the cooler (15), and then into the tank (12) through the cooler bypass valve (13). Cooler bypass valve (14) allows higher pressure oil to bypass the cooler. Return oil from the metering pump flows directly into the tank.
Hydraulic Tank
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| Illustration 2 | g01060702 |
(12) Hydraulic tank (20) Strainer for the work tool and steering pump (21) Strainer for the pump for the fan drive and the coupler (22) Temperature sender (23) Strainer for the return line | |
The hydraulic tank (12) supplies hydraulic oil for all of the systems. The hydraulic tank is located on the right side of the machine below the cab.
Three strainers are located inside the hydraulic tank. One strainer (21) is located in the outlet to the charge pump and the fan pump. One strainer is located in the outlet to the work tool and the steering pump (20). The third strainer (23) is located in the return line. The hydraulic tank is not pressurized.
When the temperature of the hydraulic oil becomes excessive, a temperature sender (22) activates the indicator light that is located on the dash.
Gear Pump
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| Illustration 3 | g01060713 |
(9) Piston pump (10) Gear pump (24) Charge pump (25) Test ports | |
The gear pump (10) draws oil from the hydraulic tank. The gear pump is located on the right side of the engine compartment. The gear pump is splined to the piston pump ( hydrostatic) (9). The piston pump is splined to the engine crankshaft. The piston pump ( hydrostatic) and the gear pump turn at engine speed.
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| Illustration 4 | g01060733 |
(8) Solenoid valve ( coupler) (10) Gear pump (H) Work tool and steering pump (J) Pump for the fan and the coupler | |
The gear pump (10) has two sections. The first section (H) is used for the steering system and the work tool system. The second section (J) is used for the fan circuit and for the coupler. Refer to Systems Operation, "Fan Hydraulic System" for information on the operation of the fan pump. The rotation of the shaft is clockwise when the rotation of the shaft is viewed from the drive end. Test ports (25) are located on the work tool and the steering section of the pump and on the section for the fan circuit and for the coupler.
Bank Valve
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| Illustration 5 | g01060767 |
(7) Bank valve (26) Priority valve (27) Auxiliary control valve (28) Tilt control valve (29) Lift control valve (30) Outlet housing (31) Outlet port (32) Inlet housing (33) Inlet port (34) Main relief valve | |
The pilot valves (18) and (19) provide pilot pressure to the bank valve (7). The bank valve controls the following components: lift cylinder (6), tilt cylinder (5) and work tools through the auxiliary couplings (4). Refer to Systems Operation, "Pilot Hydraulic System" for information on the operation of the pilot hydraulic system.
The bank valve (7) consists of the following six sections: inlet housing (32), priority valve (26), auxiliary control valve (27), tilt control valve (28), lift control valve (29) and outlet housing (30). The inlet housing contains the inlet port (33) and the main relief valve (34). The outlet housing contains the outlet port (31) .
The priority valve (26) gives priority to the steering components (1) and (2) over the work tool. Refer to Systems Operation, "Steering System" for more information on the priority valve.
Main Relief Valve
The main relief valve (34) is located in the inlet housing (32) of the bank valve.
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| Illustration 6 | g01060769 |
View B-B Main relief valve (35) Inlet passage (36) Valve (37) Passage to tank (38) Spring (39) Cap (40) Locknut (41) Adjusting screw | |
Pressure oil flows into passage (35). The oil acts against the left side of valve (36), which is held closed by spring (38) .
When an outside force causes pressure in any of the cylinders to rise, the increase in pressure is also sensed in passage (35). As the pressure rises above the pressure setting, the oil overcomes the force of spring (38) and valve (36) will move to the right.
Oil in passage (35) then flows past the open valve, through passage (37), into the outlet housing (30) and through outlet port (31) .
The pressure in the cylinders cannot increase further. When oil pressure returns to a level below the pressure setting, spring (38) moves valve (36) to the left and onto the seat.
The relief valve pressure setting can be adjusted by removing the cap (39) and loosening locknut (40). Turn adjusting screw (41) clockwise in order to increase the pressure setting. Turn adjusting screw (41) counterclockwise in order to decrease the pressure setting. After adjustment, tighten the locknut (40) and install the cap (39). Refer to Testing and Adjusting, "Main Relief Valve - Test and Adjust" for information on the testing and adjustment of the main relief valve.
Lift Control Valve (HOLD Position)
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| Illustration 7 | g01060887 |
View E-E (29) Lift control valve (42) Makeup valve for the rod end of the lift cylinder (43) Port to the rod end of the lift cylinder (44) Passage (45) Parallel passage (46) Check valve (47) Port to the head end of the lift cylinder (48) Relief valve (49) Spacer (50) Port from the pilot valve (51) Spring (52) Spool (53) Passage (54) Supply passage (55) Passage to the outlet housing (56) Supply passage (57) Passage (58) Passage to the hydraulic tank (59) Spring (60) Port from the pilot valve | |
The lift control valve (29) controls the lift cylinder. The lift control valve has the following four positions: HOLD, RAISE, LOWER and FLOAT.
The oil flows from the inlet housing (32) through the auxiliary control valve (27), through the tilt control valve (28), and into supply passages (54) and (56). The oil also flows into the parallel passage (45). When the lift control valve is in the HOLD position, the oil flows around valve spool (52) and into passage (55). The oil then flows into the outlet housing (30) and through the outlet port (31) .
When the lift control valve is in the HOLD position, valve spool (52) blocks the flow of oil into ports (43) and (47). The oil in the circuits to the lift cylinder is stopped. The spring (51) holds the spool (52) centered when no pilot oil is routed to the spool. The lift cylinders cannot move until the pilot control lever and the valve spool are moved to the RAISE position, to the LOWER position, or to the FLOAT position.
Lift Control Valve (RAISE Position)
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| Illustration 8 | g01060896 |
View E-E (29) Lift control valve (42) Makeup valve for the rod end of the lift cylinder (43) Port to the rod end of the lift cylinder (44) Passage (45) Parallel passage (46) Check valve (47) Port to the head end of the lift cylinder (48) Relief valve (49) Spacer (50) Port from the pilot valve (51) Spring (52) Spool (53) Passage (54) Supply passage (55) Passage to the outlet housing (56) Supply passage (57) Passage (58) Passage to the hydraulic tank (59) Spring (60) Port from the pilot valve | |
When the operator moves the pilot valve for the implements to the RAISE position, pilot oil flows from the pilot valve to port (60). The pilot oil overcomes the force of the spring (51). The spool (52) shifts to the left. Pilot oil in port (50) flows to the hydraulic tank.
When valve spool (52) moves to the left and into the RAISE position, supply oil from passages (54) and (56) is blocked from entering the passage to the outlet housing (55). The oil pressure in passage (45) increases until check valve (46) opens. When the check valve opens, the pump oil in passage (45) flows through the check valve, into passages (44) and (57), and out of port (47). Then, the oil flows to the head end of the lift cylinder.
The pump oil that is flowing into the head end of the lift cylinder extends the cylinder rod and the work tool rises. Return oil from the rod end of the lift cylinder flows through port (43), through passage (53) through passage (58), and to the hydraulic tank.
A relief valve (48) for the head end is mounted in the lift control valve.
When the operator releases the pilot valve for the implements to the HOLD position, pilot oil to port (60) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (51) returns the spool to the center position. The lift control valve is in the HOLD position.
Lift Control Valve (LOWER Position)
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| Illustration 9 | g01060900 |
View E-E (29) Lift control valve (42) Makeup valve for the rod end of the lift cylinder (43) Port to the rod end of the lift cylinder (44) Passage (45) Parallel passage (46) Check valve (47) Port to the head end of the lift cylinder (48) Relief valve (49) Spacer (50) Port from the pilot valve (51) Spring (52) Spool (53) Passage (54) Supply passage (55) Passage to the outlet housing (56) Supply passage (57) Passage (58) Passage to the hydraulic tank (59) Spring (60) Port from the pilot valve | |
When the operator moves the pilot valve for the implements to the LOWER position, pilot oil flows from the pilot valve and into port (50). The pilot oil overcomes the force of the spring (51). The spool (52) shifts to the right until the spool contacts the spacer (49). With the control lever of the pilot valve in the LOWER position, the pilot oil cannot overcome the force of the spring (59). The spool remains in this position. Pilot oil in port (60) flows to the hydraulic tank.
When valve spool (52) moves to the right and into the LOWER position, supply oil from passages (54) and (56) is blocked from entering the passage to the outlet housing (55). The oil pressure in passage (45) increases until check valve (46) opens. When the check valve opens, the pump oil in passage (45) flows through the check valve, into passages (44) and (53), and out of port (43). Then, the oil flows to the rod end of the lift cylinder.
The pump oil that is flowing into the rod end of the lift cylinder retracts the cylinder rod and the work tool lowers. Return oil from the head end of the lift cylinder flows through port (47), through passage (57) through passage (58), and to the hydraulic tank.
A makeup valve (42) is mounted in passage (43) to the rod end of the lift cylinder. The makeup valve functions when the control valve spool is in the FLOAT position or in the LOWER position.
Spring force combines with the oil pressure in the spring chamber in order to hold makeup valve (42) closed. The makeup valve opens only when the pump can not supply enough oil to the lift cylinder. This prevents cavitation in the lift cylinder.
When not enough oil is being supplied to the rod end of the lift cylinder, the oil pressure in passage (43) is low. The higher pressure of the return oil that is in the passages (57) and (58) to the hydraulic oil tank opens the makeup valve. This allows more oil to flow to the rod end of the lift cylinder.
The main relief valve (34) in the inlet housing (32) serves as the relief valve for the rod end of the lift cylinder.
When the operator releases the pilot valve for the implements to the HOLD position, pilot oil to port (50) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (51) returns the spool to the center position. The lift control valve is in the HOLD position.
Lift Control Valve (FLOAT Position)
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| Illustration 10 | g01060915 |
View E-E (29) Lift control valve (42) Makeup valve for the rod end of the lift cylinder (43) Port to the rod end of the lift cylinder (44) Passage (45) Parallel passage (46) Check valve (47) Port to the head end of the lift cylinder (48) Relief valve (49) Spacer (50) Port from the pilot valve (51) Spring (52) Spool (53) Passage (54) Supply passage (55) Passage to the outlet housing (56) Supply passage (57) Passage (58) Passage to the hydraulic tank (59) Spring (60) Port from the pilot valve | |
When the operator moves the pilot valve for the implements to the FLOAT position, pilot oil flows from the pilot valve and into port (50). The pilot oil overcomes the force of the spring (51). The spool (52) shifts to the right until the spool contacts the spacer (49). The pilot oil overcomes the spring (59) and the spool pushes the spacer to the right.
The pilot valve has a detent in this position. This allows the control lever and the lift control valve to remain in the FLOAT position until the control lever is pulled out of the detent.
When valve spool (52) moves to the right and into the FLOAT position, supply oil from passages (54) and (56) is blocked from entering the passage to the outlet housing (55). The position of the spool allows oil in passage (58) to flow to passages (53) and (57) and to ports (43) and (47). When the pressure in both ends of the lift cylinder is equal, the weight of the boom and of the work tool causes the work tool to lower to the ground.
While the pilot valve for the implements and the lift control valve are in the FLOAT position, the bucket will move along the contour of the ground during machine travel.
When the operator pulls the pilot valve for the implements out of the detent and the operator releases the pilot valve to the HOLD position, the pilot oil to port (50) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (51) returns the spool to the center position. The lift control valve is in the HOLD position.
Tilt Control Valve (HOLD Position)
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| Illustration 11 | g01060921 |
View D-D (28) Tilt control valve (61) Relief valve and makeup valve (62) Port to the rod end of the tilt cylinder (63) Passage (64) Check valve (65) Parallel passage (66) Port to the head end of the tilt cylinder (67) Relief valve and makeup valve (68) Port from the pilot valve (69) Spring (70) Spool (71) Passage (72) Supply passage (73) Passage to the lift control valve (74) Supply passage (75) Passage (76) Passage to the hydraulic oil tank (77) Spring (78) Port from the pilot valve | |
The tilt control valve (28) controls the tilt cylinder. The tilt control valve has the following three positions: HOLD, TILT BACK and DUMP.
The oil flows from the inlet housing (32) through the auxiliary control valve (27), and into supply passages (72) and (74). The oil also flows into the parallel passage (65). When the lift control valve (29) is in the HOLD position, the oil flows around valve spool (70) and into passage (73). The oil then flows through the lift control valve, into the outlet housing (30), and through the outlet port (31) .
When the tilt control valve is in the HOLD position, valve spool (70) blocks the flow of oil in ports (62) and (66). The oil in the circuits to the tilt cylinder is stopped. The springs (69) and (77) hold the spool centered when no pilot oil is routed to the spool. The tilt cylinder cannot move until the pilot control lever and the valve spool are moved to the TILT BACK position or to the DUMP position.
Tilt Control Valve (TILT BACK Position)
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| Illustration 12 | g01060922 |
View D-D (28) Tilt control valve (61) Relief valve and makeup valve (62) Port to the rod end of the tilt cylinder (63) Passage (64) Check valve (65) Parallel passage (66) Port to the head end of the tilt cylinder (67) Relief valve and makeup valve (68) Port from the pilot valve (69) Spring (70) Spool (71) Passage (72) Supply passage (73) Passage to the lift control valve (74) Supply passage (75) Passage (76) Passage to the hydraulic oil tank (77) Spring (78) Port from the pilot valve | |
When the operator moves the pilot valve for the implements to the TILT BACK position, pilot oil flows from the pilot valve to port (78). The pilot oil overcomes the force of the spring (69). The spool (70) shifts to the left. Pilot oil in port (68) flows to the hydraulic tank.
When valve spool (70) moves to the left and into the TILT BACK position, supply oil from passages (72) and (74) is blocked from entering the passage (73) to the lift control valve (29). The oil pressure in the parallel passage (65) increases until check valve (64) opens. When the check valve opens, the pump oil in passage (65) flows through the check valve, into passages (63) and (75), and out of port (66). Then, the oil flows to the rod end of the tilt cylinder.
The pump oil that is flowing into the rod end of the tilt cylinder retracts the cylinder rod and the work tool tilts back. Return oil from the head end of the tilt cylinder flows through port (62), through passage (71) through passage (76), and to the hydraulic tank.
A relief valve and makeup valve (67) for the rod end is mounted in the tilt control valve.
When the operator releases the pilot valve for the implements to the HOLD position, pilot oil to port (78) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (69) returns the spool to the center position. The tilt control valve is in the HOLD position.
Tilt Control Valve (DUMP Position)
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| Illustration 13 | g01060923 |
View D-D (28) Tilt control valve (61) Relief valve and makeup valve (62) Port to the rod end of the tilt cylinder (63) Passage (64) Check valve (65) Parallel passage (66) Port to the head end of the tilt cylinder (67) Relief valve and makeup valve (68) Port from the pilot valve (69) Spring (70) Spool (71) Passage (72) Supply passage (73) Passage to the lift control valve (74) Supply passage (75) Passage (76) Passage to the hydraulic oil tank (77) Spring (78) Port from the pilot valve | |
When the operator moves the pilot valve for the implements to the DUMP position, pilot oil flows from the pilot valve to port (68). The pilot oil overcomes the force of the spring (77). The spool (70) shifts to the right. Pilot oil in port (78) flows through the line to the hydraulic tank.
When the valve spool moves to the right and into the DUMP position, supply oil from passages (72) and (74) is blocked from entering the passage (73) to the lift control valve (29). The oil pressure in the parallel passage (65) increases until check valve (64) opens. When the check valve opens, the pump oil in passage (65) flows through the check valve, and into passages (63), (71), and (75). The rod end of the tilt cylinder and the head end of the tilt cylinder are connected through ports (62) and (66). With the valve spool in this position, the pump flow is supplemented by rod end oil. This prevents cavitation in the head end of the tilt cylinder. The oil flows into the head end of the tilt cylinder and the work tool is dumped.
A relief valve and makeup valve (61) for the head end is mounted in the tilt control valve.
When the operator releases the pilot valve for the implements to the HOLD position, pilot oil to port (68) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (77) returns the spool to the center position. The tilt control valve is in the HOLD position.
Auxiliary Control Valve (HOLD Position)
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| Illustration 14 | g01060929 |
View C-C (27) Auxiliary control valve (79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (85) Port from the pilot valve (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (95) Port from the pilot valve | |
The auxiliary control valve (27) controls the auxiliary circuit. The auxiliary control valve has the following three positions: HOLD, ON for the right hand side auxiliary coupling and ON for the left hand side auxiliary coupling.
The oil flows from the inlet housing (32) into supply passages (89) and (91). The oil also flows into the parallel passage (83). When the auxiliary control valve is in the HOLD position, the oil flows around valve spool (87) and into passage (90). The oil then flows through the tilt control valve (28), through the lift control valve (29), into the outlet housing (30) and through the outlet port (31) .
When the auxiliary control valve is in the HOLD position, valve spool (87) blocks the flow of oil in ports (80) and (84). The oil in the auxiliary circuits is stopped. The springs (86) and (94) hold the spool centered when no pilot oil is routed to the spool. The auxiliary circuit does not receive oil until the control lever is moved to an ON position.
Auxiliary Control Valve (ON Position for the Right Hand Side Auxiliary Coupling)
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| Illustration 15 | g01060939 |
View C-C (27) Auxiliary control valve (79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (85) Port from the pilot valve (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (95) Port from the pilot valve | |
When the operator moves the pilot valve to the ON position for the right hand side auxiliary coupling, pilot oil flows from the pilot valve to port (96). The pilot oil overcomes the force of the spring (86). The spool (87) shifts to the left. Pilot oil in port (85) flows to the hydraulic tank.
When valve spool (87) moves to the left and into the ON position for the right hand side auxiliary coupling, supply oil from passages (89) and (91) is blocked from entering the passage (90) to the tilt control valve. The oil pressure in the parallel passage (83) increases until check valve (82) opens. When the check valve opens, the pump oil in passage (83) flows through the check valve, into passages (81) and (92), and out of port (84). Then, the oil flows to the right hand side auxiliary coupling (5) .
Return oil from the left hand auxiliary circuit flows through port (80), through passage (88) through passage (93), and to the hydraulic tank.
A relief valve and makeup valve (79) is mounted in the auxiliary control valve.
The operator can move the pilot valve to the DETENT position. The auxiliary control valve will remain in the ON position for the right hand side auxiliary coupling and the auxiliary line will receive constant flow. This allows the control lever and the auxiliary control valve to remain in the ON position for the right hand side auxiliary coupling until the control lever is pulled out of the detent. When the operator pulls the control lever of the pilot valve out of the detent and the operator releases the control lever of the pilot valve to the HOLD position, pilot oil to port (96) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (86) returns the spool to the center position. The auxiliary control valve is in the HOLD position.
Auxiliary Control Valve (ON Position for the Left Hand Side Auxiliary Coupling)
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| Illustration 16 | g01060946 |
View C-C (27) Auxiliary control valve (79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (85) Port from the pilot valve (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (95) Port from the pilot valve | |
When the operator moves the control lever of the pilot valve to the ON position for the left hand side auxiliary coupling, pilot oil flows from the pilot valve to port (85). The pilot oil overcomes the force of the spring (94). The spool (87) shifts to the right. Pilot oil in port (96) flows to the hydraulic tank.
When valve spool (87) moves to the right and into the ON position for the left hand side auxiliary coupling, supply oil from passages (89) and (91) is blocked from entering the passage (90) to the tilt control valve. The oil pressure in the parallel passage (83) increases until check valve (82) opens. When the check valve opens, the pump oil in passage (83) flows through the check valve, into passages (81) and (88), and out of port (80). Then, the oil flows to the left hand side auxiliary circuit.
Return oil from the left hand auxiliary circuit flows through port (84), through passage (92) through passage (93), and to the hydraulic tank.
A relief valve and makeup valve (79) for the auxiliary circuit is mounted in the auxiliary control valve.
When the operator releases the control lever of the pilot valve to the HOLD position, pilot oil to port (85) stops. The pilot oil lines are open to the hydraulic tank. With no pilot pressure, the spring (94) returns the spool to the center position. The auxiliary control valve is in the HOLD position.
Cooler
The oil flows from the outlet port (31) to the cooler bypass valve (14) and the cooler (15). The cooler uses air to cool the hydraulic oil. The cooler is located behind an access panel on the left side of the machine. The cooler dissipates heat from the hydraulic system in order to prevent overheating.
Cooler Bypass Valve ( High Pressure)
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| Illustration 17 | g01060970 |
(14) Cooler bypass valve ( high pressure) (96) Poppet (97) Spring (98) Inlet (99) Outlet | |
The cooler bypass valve ( high pressure) (14) allows higher pressure oil to flow around the cooler and to the hydraulic tank. The higher pressure oil occurs when the oil is cold.
The oil flows into the inlet (98). When the oil pressure overcomes the force of spring (97), the poppet (96) moves to the right and the oil flows through the outlet (99) and to the hydraulic tank.
Cooler Bypass Valve ( Low Pressure)
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| Illustration 18 | g01060998 |
(13) Cooler bypass valve ( low pressure) (100) Poppet (101) Spring (102) Inlet (103) Outlet | |
The oil flows from the cooler (15) to a cooler bypass valve ( low pressure) (13) and to the bearings in the piston motor (G). The check valve allows back pressure at the cooler. The back pressure causes oil to flow to the bearings in the piston motor.
The oil flows into the inlet (102). When the oil pressure overcomes the force of spring (101), the poppet (100) moves to the right and the oil flows through the outlet (103) and to the hydraulic tank.
Work Tool Positioner Solenoid (if equipped)
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| Illustration 19 | g01061043 |
(17) Solenoid valve ( pilot shutoff) (28) Tilt control valve (104) Work tool positioner solenoid (A) Hystat charge oil and pilot supply oil (B) Hystat supply (C) Hystat supply (G) Supply oil to the bearing for the piston motor (K) Supply line to the couplers (L) Oil pressure from the load sensing port on the metering pump (M) Oil pressure from the metering pump | |
The work tool positioner allows the operator to return the work tool to a preset angle after the operator dumps the load. The pilot shutoff solenoid (17) must be energized in order for the system to function.
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| Illustration 20 | g01061109 |
(105) Switch for the work tool positioner | |
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| Illustration 21 | g01061111 |
(106) Button for the work tool positioner | |
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| Illustration 22 | g01061114 |
(107) Sensor (108) Magnet | |
The switch (105) for the work tool positioner must be ON in order to activate the work tool positioner. When the switch is ON and the button (106) is pressed, a relay is activated. When the relay energizes, the solenoid (104) activates. This allows pilot oil to flow to the tilt control valve (28) in order to rack back the work tool. When the sensor (107) is aligned with the magnet (108), a signal is sent in order to de-energize the relay. This causes the solenoid to deactivate. This prevents the work tool from racking back further.
Note: If the work tool positioner is activated with the work tool already in the preset digging angle, the work tool will rack back until the timer deactivates. The timer lasts for five seconds. This may cause the line relief valves for the tilt cylinder to shift.
The return angle of the work tool can be changed by moving the magnet upward on the rod of the tilt cylinder or downward on the rod of the tilt cylinder. Moving the magnet farther down the rod will cause the work tool to rack back further. Moving the magnet farther up the rod will cause the work tool to rack back less.
Load Check Valves (if equipped)
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| Illustration 23 | g01061117 |
(109) Load check valve for the tilt cylinder (110) Load check valve for the lift cylinder (111) Hand pump for lowering the work tool with a dead engine (A) Hystat charge oil and pilot supply oil (B) Hystat supply (C) Hystat supply (G) Supply oil to the bearing for the piston motor (K) Supply line to the couplers (L) Oil pressure from the load sensing port on the metering pump (M) Oil pressure from the metering pump | |
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| Illustration 24 | g01061125 |
(109) Load check valve for the tilt cylinder | |
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| Illustration 25 | g01061127 |
(110) Load check valve for the lift cylinder | |
Load check valves (109) and (110) prevent the work tool from moving if the engine fails. The load check valves also prevent cylinder drift. The load check valves are pilot operated check valves.
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| Illustration 26 | g01061132 |
(110) Load check valve for the tilt cylinder (112) Pilot operated check valve (113) Check valve (114) Relief valve | |
When the pilot valve for the implements is moved to the LOWER position pilot oil flows from the pilot valve for the implements to the bank valve in order to shift the lift control valve to the LOWER position. Some of the pilot oil flows to the load check valve for the lift cylinder in order to shift valve (112). This allows oil to flow freely to the rod end of the lift cylinder.
When the pilot valve for the implements is moved to the RAISE position pilot oil shifts the lift control valve to the RAISE position. Oil flows through the check valve (113) within the valve (112) to the head end of the lift cylinder.
When the machine loses power and the work tool is raised, pilot pressure is cut off. The valve (112) is shifted to the right by spring pressure. The load cannot drift downward because of the check valve (113). The load check valve for the tilt cylinder works in the same manner as the load check valve for the lift cylinder.
Use the following procedure in order to lower the work tool with a dead engine.
- Open the bypass valve (115) on the lift control valve (29) .
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| Illustration 27 | g01061140 |
(29) Lift control valve (115) Bypass valve | |
- Open the bypass valve (116) on the hand pump (111) that is located in the articulation joint on the right side of the machine. Operate the hand pump by moving the rod (117) in and out of the hand pump. The work tool will begin to lower when the hand pump is first operated.
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| Illustration 28 | g01061157 |
(111) Hand pump (116) Screw for the bypass on the hand pump (117) Rod | |
- After the work tool is lowered to the ground, the bypass valve on the hand pump must be turned all the way out of the hand pump. The rod must be pulled out to the original position. The screw for the bypass on the lift control valve (116) must be turned counterclockwise to the original position.
Proportional Auxiliary Circuit Control (if equipped)
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| Illustration 29 | g01061174 |
(4) Auxiliary couplings (118) Modulating valve (119) Modulating valve (A) Hystat charge oil and pilot supply oil (G) Supply oil to the bearing for the piston motor (K) Supply line to the couplers (L) Oil pressure from the load sensing port on the metering pump (M) Oil pressure from the metering pump | |
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| Illustration 30 | g01062896 |
(120) Thumb wheel for the proportional auxiliary control | |
If the machine is equipped with a proportional auxiliary circuit control, the auxiliary circuit is controlled by the thumb wheel (120) on the joystick. When you move the thumb wheel forward, modulating valve (119) shifts. This allows a proportional amount of pilot oil to flow to the spool for the auxiliary. The spool for the auxiliary shifts by a proportional amount from the pressure that is applied to the switch. A proportional amount of hydraulic oil will flow out of the left hand side auxiliary coupling.
When you move the thumb wheel (120) backward, modulating valve (118) shifts. This allows a proportional amount of pilot oil to flow to the spool for the auxiliary. The spool for the auxiliary shifts by a proportional amount from the pressure that is applied to the switch. A proportional amount of hydraulic oil will flow out of the right hand side auxiliary coupling.
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| Illustration 31 | g01061180 |
(121) Switch for the proportional auxiliary circuit control | |
Continuous flow to the auxiliary couplings is available by pressing the switch (121) and holding the switch that is on the control panel on the right hand side of the cab. Then, the thumb wheel (120) on the joystick should be moved and released. Lastly, the operator should release the switch on the control panel (121). Continuous oil flow should then be flowing through the auxiliary couplings. Press the switch (121) or move the thumb wheel (120) in order to stop the continuous flow.
Refer to Systems Operation, "Pilot Hydraulic System" for more information.
Auxiliary Control Valve (HOLD Position)
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| Illustration 32 | g01075995 |
(79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (118) Modulating valve (119) Modulating valve | |
The auxiliary control valve controls the auxiliary circuit. The auxiliary control valve has the following three positions: HOLD, ON for the right hand side auxiliary coupling and ON for the left hand side auxiliary coupling.
The oil flows from the inlet housing into supply passages (89) and (91). The oil also flows into the parallel passage (83). When the auxiliary control valve is in the HOLD position, the oil flows around valve spool (87) and into passage (90). The oil then flows through the tilt control valve, through the lift control valve, into the outlet housing and through the outlet port .
When the auxiliary control valve is in the HOLD position, valve spool (87) blocks the flow of oil in ports (80) and (84). The oil in the auxiliary circuits is stopped. The springs (86) and (94) hold the spool centered when no pilot oil is routed to the spool. The auxiliary circuit does not receive oil until the thumb wheel is moved to an ON position.
Auxiliary Control Valve (ON Position for the Right Hand Side Auxiliary Coupling)
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| Illustration 33 | g01076076 |
(79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (118) Modulating valve (119) Modulating valve | |
When you move the thumb wheel backward, modulating valve (118) shifts. This allows a proportional amount of pilot oil to flow to the spool for the auxiliary (87). The spool for the auxiliary shifts by a proportional amount from the pressure that is applied to the switch. Pilot oil flows through modulating valve (118). The pilot oil overcomes the force of the spring (86). The spool (87) shifts to the left. Pilot oil is blocked at modulating valve (119) .
When valve spool (87) moves to the left and into the ON position for the right hand side auxiliary coupling, supply oil from passages (89) and (91) is blocked from entering the passage (90) to the tilt control valve. The oil pressure in the parallel passage (83) increases until check valve (82) opens. When the check valve opens, the pump oil in passage (83) flows through the check valve, into passages (81) and (92), and out of port (84). Then, the oil flows to the right hand side auxiliary circuit.
Return oil from the right hand auxiliary circuit flows through port (80), through passage (88) through passage (93), and to the hydraulic tank.
Makeup and relief valves (79) for the auxiliary circuit are mounted in the auxiliary control valve.
When the operator releases the thumb wheel, modulating valve (118) returns to the HOLD position. Pilot oil is blocked at modulating valves (118) and (119). With no pilot pressure, the spring (86) returns the spool to the center position. The auxiliary control valve is in the HOLD position.
Auxiliary Control Valve (ON Position for the Left Hand Side Auxiliary Coupling)
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| Illustration 34 | g01076103 |
(79) Makeup and relief valve (80) Port to the left hand side of the auxiliary circuit and port to the rod end of the coupler cylinders (81) Passage (82) Check valve (83) Parallel passage (84) Port to the right hand side auxiliary circuit (86) Spring (87) Spool (88) Passage (89) Supply passage (90) Passage to the tilt control valve (91) Supply passage (92) Passage (93) Passage to the hydraulic oil tank (94) Spring (118) Modulating valve (119) Modulating valve | |
When you move the thumb wheel forward, modulating valve (119) shifts. This allows a proportional amount of pilot oil to flow to the spool for the auxiliary (87). The spool for the auxiliary shifts by a proportional amount from the pressure that is applied to the switch. Pilot oil flows through modulating valve (119). The pilot oil overcomes the force of the spring (94). The spool (87) shifts to the right. Pilot oil is blocked at modulating valve (118) .
When valve spool (87) moves to the right and into the ON position for the left hand side auxiliary coupling, supply oil from passages (89) and (91) is blocked from entering the passage (90) to the tilt control valve. The oil pressure in the parallel passage (83) increases until check valve (82) opens. When the check valve opens, the pump oil in passage (83) flows through the check valve, into passages (81) and (88), and out of port (80). Then, the oil flows to the left hand side auxiliary circuit.
Return oil from the left hand auxiliary circuit flows through port (84), through passage (92) through passage (93), and to the hydraulic tank.
Makeup and relief valves (79) for the auxiliary circuit are mounted in the auxiliary control valve.
When the operator releases the thumb wheel, modulating valve (119) returns to the HOLD position. Pilot oil is blocked at modulating valves (118) and (119). With no pilot pressure, the spring (94) returns the spool to the center position. The auxiliary control valve is in the HOLD position.