938G Series II Wheel Loader and IT38G Series II Integrated Toolcarrier Hydraulic System Main Control Valve - IT38G Series II Integrated Toolcarrier Caterpillar


Main Control Valve - IT38G Series II Integrated Toolcarrier
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938G Series II Wheel Loader and IT38G Series II <BR>Integrated Toolcarrier Hydraulic System [RENR6077]
HYDRAULIC SYSTEM
VALVE GP-CONTROL
938G Series II Wheel Loader and IT38G Series II Integrated Toolcarrier Hydraulic System Main Control Valve - IT38G Series II Integrated Toolcarrier
1.1. Tilt Control Valve
2.2. HOLD Position
3.2. TILTBACK position
4.2. REGENERATIVE Position
5.1. Lift Control Valve
6.2. HOLD Position
7.2. RAISE Position
8.2. LOWER position
9.2. FLOAT Position
10.1. Auxiliary Control Valve
11.2. HOLD Position
12.2. OPEN Position
13.2. CLOSE Position
14.1. Fourth Function (If Equipped)

The main control valve controls the flow of high pressure oil to the implement cylinders or to a work tool. On the IT38G Series II Integrated toolcarrier, the main control valve is located in the loader frame. Access to the main control valve is through the loader tower access panel that is located on the front of the loader frame.




Illustration 1g00936124

Third Function Valve

(1) Dump. (2) Tilt back. (3) Lift raise. (4) Lift lower or float. (5) Auxiliary (open). (6) Main relief valve. (7) Auxiliary (close).




Illustration 2g00936125

Fourth Function Control Valve

(1) Dump. (2) Tilt back. (3) Lift raise. (4) Lift lower or float. (5) Auxiliary (open). (6) Main relief valve. (7) Auxiliary (close). (8) Plug. (9) Auxiliary. (10) Auxiliary.

The standard IT38G Series II Integrated Toolcarrier is equipped with a third function valve. The third function valve controls the lift, tilt and the auxiliary functions. The machine may also be equipped with a fourth function control valve. This valve will control the operation of an extra auxiliary function.

The implement pump supplies the hydraulic oil to the main control valve. As high pressure oil enters the main control valve, the oil passes over main relief valve (6). Main relief valve (6) limits the oil pressure that is supplied by the implement pump. When the oil pressure at the inlet of the main control valve exceeds the pressure setting of main relief valve (6), the relief valve opens. The pressure that is above the adjusted pressure will flow through the main relief valve to the hydraulic tank. The system pressure flows to the stems of the main control valve through common ports.

If the machine is equipped with a fourth function control valve, plug (8) will be installed in the auxiliary valve section. Main relief valve (6) will be installed in the fourth function control valve.

Reference: For additional information on the main relief valve, refer to the Service Manual module Systems Operation and Testing and Adjusting, " Relief Valve - Main" for the machine that is being serviced.

The stems in the main control valve are open centered. When the control levers for the pilot valve are in the HOLD position, no pilot oil will flow to any pilot ports on the main control valve. The stems of the main control valve are in the HOLD position. The hydraulic oil flows through the main control valve and back to the hydraulic tank.

Tilt Control Valve

HOLD Position




Illustration 3g00939246

(11) Pilot port (dump). (12) Outlet. (13) Pilot port (tilt back). (14) Tilt stem. (15) Inlet. (16) Spring. (17) Spring. (18) Line relief valve. (19) Tank passage. (20) Bridge passage. (21) Series feeder passage. (22) Tank passage. (23) Line relief valve. (24) Check valve.

When the tilt control lever on the pilot valve is in the HOLD position, no pilot oil is flowing to either pilot port of the tilt valve section. Spring (16) and spring (17) at either end of tilt stem (14) maintain tilt stem (14) in the HOLD position.

In the HOLD position, the lift valve section is open centered. Pump supply oil enters the tilt valve section through inlet (15) by way of the auxiliary valve section. Then, the pump supply oil flows around the center land of tilt stem (14) to outlets (12). Outlet (12) supplies the hydraulic oil with a path through the lift valve section. Then, the oil flows to the hydraulic tank. At this time, no oil is flowing to the port for the rod end or the port for the head end. The oil in the port for the rod end and the oil in the port for the head end is trapped in the system between the tilt stem within the tilt valve section and the tilt cylinder.

At this time, no oil is flowing to the port for the rod end or the port for the head end. The oil in the port for the rod end and the oil in the port for the head end is trapped in the system between the tilt stem within the tilt valve section and the tilt cylinder.

TILTBACK position




Illustration 4g00939380

(11) Pilot port (dump). (12) Outlet. (13) Pilot port (tilt back). (14) Tilt stem. (15) Inlet. (16) Spring. (17) Spring. (18) Line relief valve. (19) Tank passage. (20) Bridge passage. (21) Series feeder passage. (22) Tank passage. (23) Line relief valve. (24) Check valve.

When the tilt lever on the pilot valve is placed in the TILT BACK position, pilot oil is flowing to the pilot port (tilt back) (13). The pilot pressure overrides the force of spring (16). Tilt stem (14) shifts to the left.

Pump supply oil flows into the tilt valve section by way of the auxiliary valve section through inlet (15). The pump supply oil that was flowing around tilt stem (14) to outlets (12) is now blocked. Pump supply oil flows from inlet (15) through series feeder passage (21). When the oil pressure in the series feeder passage (21) is greater than the combination of the oil pressure in bridge passage (20) and the force of the spring in check valve (24), the pump supply oil will override the force of the spring in check valve (24). Check valve (24) will open.

Then, the oil flows through bridge passage (20), around tilt stem (14), and into the port for the rod end. The oil in the port for the rod end flows to the rod end of the tilt cylinders. The oil in the port for the head end flows through the grooves in lift stem (14), to tank passage (19), and to the hydraulic tank. The work tool begins to tilt back.

REGENERATIVE Position




Illustration 5g00939259

(11) Pilot port (dump). (12) Outlet. (13) Pilot port (tilt back). (14) Tilt stem. (15) Inlet. (16) Spring. (17) Spring. (18) Line relief valve. (19) Tank passage. (20) Bridge passage. (21) Series feeder passage. (22) Tank passage. (23) Line relief valve. (24) Check valve. (25) Land.

When the tilt lever on the pilot valve is placed into the full DUMP position, pilot oil is flowing to the pilot port (dump) on the left side of the tilt valve section. Tilt stem (14) is shifted completely to the right.

As the tilt lever on the pilot valve moves to the full DUMP position, pump supply oil enters the main control valve and flows to inlet (15). Pump supply oil flows from inlet (15) through series feeder passage (21). The force of the oil that is flowing from inlet (15) will override the force of the spring in check valve (24). Check valve (24) opens. The pump supply oil flows around tilt stem (14) to the port for the head end. The work tool begins to dump. During a dump operation, the weight transfer of the bucket will place a download force on the rod end of the tilt cylinders. The pressure at the port for the head end begins to rise because the oil in the port for the rod end to tank passage (22) is blocked by land (25). Then, the secondary source of oil in the port for the rod end flows around the stem (14) and into bridge passage (20). The oil in the port for the rod end flows together with pump supply oil. This will assist the implement pump in filling a void in the port for the head end with hydraulic oil.

Lift Control Valve

HOLD Position




Illustration 6g00938962

(26) Pilot port (raise). (27) Outlets. (28) Pilot port (lower or float). (29) Lift stem. (30) Inlet. (31) Restriction. (32) Spring. (33) Tank passage. (34) Bridge passage. (35) Series feeder passage. (36) Tank passage. (37) Makeup valve. (38) Spring. (39) Check valve.

When the levers on the pilot valve are in the HOLD position, no pilot oil is flowing to the end caps of the main control valve. Spring (32) and spring (38) at either end of lift stem (29) maintain lift stem (29) in the HOLD position.

In the HOLD position, the lift valve section is open centered. Pump supply oil enters the lift valve section through inlet (30) by way of the tilt valve section. Then, the oil flows around the center land of the lift stem (29) to outlets (27). Outlets (27) supply a path for the hydraulic oil to travel from the lift valve section and into the hydraulic tank.

At this time, no oil will be flowing to either the port for the head end or to the port for the rod end. The oil in the port for the head end and the oil in the port for the rod end will be trapped in the system between lift stem (29) within the lift valve section and the lift cylinder.

RAISE Position




Illustration 7g00938992

(26) Pilot port (raise). (27) Outlets. (28) Pilot port (lower or float). (29) Lift stem. (30) Inlet. (31) Restriction. (32) Spring. (33) Tank passage. (34) Bridge passage. (35) Series feeder passage. (36) Tank passage. (37) Makeup valve. (38) Spring. (39) Check valve.

When the lift lever on the pilot valve is placed in the RAISE position, pilot oil is flowing to the pilot port (raise) (26) on the left side of the lift valve section. The pilot pressure overrides the force of spring (38). Lift stem (29) shifts to the right.

Pump supply oil flows into the lift valve section through inlet (30). The pump supply oil that was flowing around lift stem (29) to outlets (27) is blocked. Pump supply oil flows from inlet (30) into series feeder passage (35). When the oil pressure in series feeder passage (35) becomes greater than the combination of the oil pressure in bridge passage (34) and the force of the spring in check valve (39). The force of the hydraulic oil that is flowing from inlet (30) will override the spring force in check valve (39). Check valve (39) opens.

The pump supply oil flows through bridge passage (34), around the lift stem (29), and into the port for the head end. The oil in the port for the head end flows to the head end of the lift cylinders. The oil in the port for the rod end flows through the grooves in lift stem (29), to tank passage (36), and to the hydraulic tank. The lift arms began to raise.

LOWER position




Illustration 8g00939001

(26) Pilot port (raise). (27) Outlets. (28) Pilot port (lower or float). (29) Lift stem. (30) Inlet. (31) Restriction. (32) Spring. (33) Tank passage. (34) Bridge passage. (35) Series feeder passage. (36) Tank passage. (37) Makeup valve. (38) Spring. (39) Check valve.

When the lift lever on the pilot valve is placed in the LOWER position, pilot oil is flows to the pilot port (lower or float) (28) on the right side of the lift valve section. The pilot pressure overrides the force of spring (32). Lift stem (29) shifts to the left.

Pump supply oil flows into the lift valve section through inlet (30). The pump supply oil that was flowing around lift stem (29) to outlets (27) is blocked. Pump supply oil flows from inlet (30) into series feeder passage (35). When the oil pressure in series feeder passage (35) becomes greater than the combination of the oil pressure in bridge passage (34) and the force of the spring in check valve (39). The force of the hydraulic oil that is flowing from inlet (30) will override the spring force in check valve (39). Check valve (39) opens.

The oil flows through bridge passage (34), around lift stem (29), and into the port for the rod end. The oil in the port for the rod end flows to the rod end of the lift cylinder. The oil in the port for the head end flows through the grooves in lift stem (29), to tank passage (33), and to the hydraulic tank. The lift arms start to lower.

If the lift lever is moved in the LOWER position too fast, the lift arms will lower at a higher rate. The lift cylinder rod retracts too fast, and the implement pump can not supply enough oil flow to the rod end of the lift cylinder. The pressure within the port for the rod end starts to decrease. When the pressure in the port for the rod end is less than the pressure in tank passage ( 36), the force on the makeup spool (37) is increased. The force on makeup valve (37) will allow the oil to override the force of the spring in makeup valve (37). The makeup spool will move and makeup valve (37) will open. The oil in tank passage (36) will flow around makeup valve (37) and into the port for the rod end. The addition of oil to the port for the rod end will help fill a void in that port. This will prevent damage from cavitation in the hydraulic system.

FLOAT Position




Illustration 9g00939031

(26) Pilot port (raise). (27) Outlets. (28) Pilot port (lower or float). (29) Lift stem. (30) Inlet. (31) Restriction. (32) Spring. (33) Tank passage. (34) Bridge passage. (35) Series feeder passage. (36) Tank passage. (37) Makeup valve. (38) Spring. (39) Check valve.

When the lift lever on the pilot valve is placed in the FLOAT position, an increased amount of pilot pressure flows to the pilot port (lower or float) (28). The pilot pressure overrides the force of spring (32). Lift stem (29) is shifted all the way to the left.

Pump supply oil flows into the lift valve section through inlet (30). The pump supply oil that was flowing around lift stem (29) to outlets (27) is blocked. Pump supply oil flows from inlet (30) into series feeder passage (35). When the oil pressure in series feeder passage (35) becomes greater than the combination of the oil pressure in bridge passage (34) and the force of the spring in check valve (39). The force of the hydraulic oil that is flowing from inlet (30) will override the spring force in check valve (39). Check valve (39) opens.

Then, the oil flows through bridge passage (34), around lift stem (29), and into port B. The restriction (31) that is built into lift stem (29) meters the oil that is flowing into tank passage (36). Metering the pump supply oil into tank passage (36) induces a minimal pressure within the port for the rod end. The minimal pressure in the port for the rod end will act on the rod end of the lift cylinders. This puts a minimal downward force on the work tool. The port for the head end is open to tank passage (33). The downward force will assist the work tool in order to follow the contour of the ground.

The lift valve section will be held in the FLOAT position until the lift lever is manually moved from the FLOAT position or the engine start switch is placed in the OFF position.

Auxiliary Control Valve

HOLD Position




Illustration 10g00939057

(40) Pilot port (auxiliary). (41) outlet. (42) Pilot port (auxiliary). (43) Auxiliary stem. (44) Inlet. (45) Spring. (46) Spring. (47) Line relief valve. (48) Tank passage. (49) Bridge passage. (50) Series feeder passage. (51) Tank passage. (52) Line relief valve. (53) Check valve.

When the auxiliary lever on the pilot valve is in the HOLD position, no pilot oil is flowing to the pilot ports of the main control valve. Spring (45) and spring (46) maintain auxiliary stem (43) in the HOLD position.

The pump supply oil enters the auxiliary valve section through inlet (44) from the implement pump. The pump supply oil that was flowing around lift stem (43) flows into outlets (41). Then, the pump supply oil flows around stem (42) to outlets (41) to the tilt valve section. Then, the pump supply oil will flow to the lift valve section and out of the main control valve.

At this time, no oil will flow to the port for the rod end or to the port for the head end. The oil in the port for the rod end and the oil in the port for the head end is trapped in the system between auxiliary stem (43) within the auxiliary valve section and the auxiliary cylinder.

OPEN Position




Illustration 11g00939123

(40) Pilot port (auxiliary). (41) outlet. (42) Pilot port (auxiliary). (43) Auxiliary stem. (44) Inlet. (45) Spring. (46) Spring. (47) Line relief valve. (48) Tank passage. (49) Bridge passage. (50) Series feeder passage. (51) Tank passage. (52) Line relief valve. (53) Check valve.

When the auxiliary lever on the pilot valve is placed in the FORWARD position, pilot oil is flowing to the pilot port (open) (40) on the left side of the lift valve section. The pilot pressure overrides the force of spring (46). Auxiliary stem (43) shifts to the right.

Pump supply oil flows into the auxiliary valve section through inlet (44). The oil that was flowing around auxiliary stem (43) to outlets (41) is blocked. Pump supply oil flows from inlet (44) into series feeder passage (50). When the oil pressure in series feeder passage (50) becomes greater than the combination of the oil pressure in bridge passage (49) and the force of the spring in check valve (53). The force of the oil that is flowing from inlet (44) will override the force of the spring in check valve (53). Check valve (53) opens.

The pump supply oil flows through bridge passage (49), around auxiliary stem (43), and into the port for the head end. The oil in the port for the head end flows to the head end of the auxiliary cylinder. The oil in the port for the rod end flows through the grooves in auxiliary stem (43), to tank passage (51), and to the hydraulic tank. The auxiliary cylinder began to open.

Line relief valve (47) is installed in the main control valve for protection against pressure spikes and/or a outside force on the work tool. If the pressure in the port for the head end becomes greater than the adjusted pressure of the line relief valve, line relief valve (47) opens. The oil flows to tank passage (47). The line relief valve will stay open, long enough for the pressure spike in the port for the head end in order to be released.

The line relief valve can also be used as a makeup valve. If the auxiliary lever is moved in the FORWARD position too fast, the attachment will move at a higher rate. The auxiliary cylinder rod retracts too fast, and the implement pump can not supply enough oil flow to the head end of the auxiliary cylinder. The pressure within the port for the head end starts to decrease. When the pressure in the port for the head end is less than the pressure in tank passage (48), the force on the makeup spool of line relief valve (47) is increased. The force on line relief valve (47) will allow the oil to override the force of the spring in line relief valve (47). The makeup spool will move and line relief valve (47) will open. Return oil will flow around line relief valve (47) into the port for the head end. This addition of oil to the port for the head end fill a void in the port for the head end.

Reference: For additional information on the line relief valve, refer to the Service Manual module Systems Operation and Testing and Adjusting, "Relief Valve (Line)" for the machine that is being serviced.

CLOSE Position




Illustration 12g00939248

(40) Pilot port (auxiliary). (41) Outlet. (42) Pilot port (auxiliary). (43) Auxiliary stem. (44) Inlet. (45) Spring. (46) Spring. (47) Line relief valve. (48) Tank passage. (49) Bridge passage. (50) Series feeder passage. (51) Tank passage. (52) Line relief valve. (53) Check valve.

When the auxiliary lever on the pilot valve is placed in the REARWARD position, the pilot oil will flow to the pilot port (close) (42). The pilot pressure overrides the force of spring (45). Auxiliary stem (43) shifts to the left.

Pump supply oil flows into the auxiliary valve section through inlet (44). The oil that was flowing around auxiliary stem (43) to outlets (41) is blocked. Pump supply oil flows from inlet (44) into series feeder passage (50). When the oil pressure in series feeder passage (50) becomes greater than the combination of the oil pressure in bridge passage (49) and the force of the spring in check valve (53). The force of the oil that is flowing from inlet (44) will override the force of the spring in check valve (53). Check valve (53) opens.

The oil flows through bridge passage (49), around auxiliary stem (43), and into the port for the rod end. The port for the rod end will be pressurized. The oil in the port for the head end flows to the auxiliary cylinder. The oil in the port for the head end flows through the grooves in auxiliary stem (43), to tank passage (51), and to the hydraulic tank. The auxiliary cylinder began to close.

Line relief valve (52) is installed in the main control valve for protection against pressure spikes and/or a outside force on the work tool. If the pressure in the port for the rod end becomes greater than the adjusted pressure of line relief valve (52), line relief valve (52) will open. Oil will flow to tank passage (51). Line relief valve (52) will stay open long enough for the pressure spike in the port for the rod end in order to be released.

If the auxiliary lever is moved in the REARWARD position too fast, the cylinder will move at a higher rate. The cylinder rod retracts too fast, and the implement pump can not supply enough oil flow to the rod end of the lift cylinder. The pressure within the port for the rod end starts to decrease. When the pressure in the port for the rod end is less than the pressure in tank passage (51), the force on the makeup spool of line relief valve (52) is increased. The force on line relief valve (52) will allow the oil to override the force of the spring in the line relief valve. The makeup valve will move and the valve will open. Return oil will flow around line relief valve (52) into the port for the rod end. This addition of oil to the port for the rod end fill a void in the port for the rod end. This will prevent damage from cavitation in the hydraulic system.

Reference: For additional information on the line relief valve, refer to the Service Manual module Systems Operation and Testing and Adjusting, "Relief Valve (Line)" for the machine that is being serviced.

Fourth Function (If Equipped)




Illustration 13g00952625

Schematic (Fourth Function)

(6) Main relief valve

(16) Stem

(18) Line relief valve

(23) Line relief valve

(29) Stem

(37) Makeup valve

(43) Stem

(47) Line relief valve

(52) Line relief valve

(54) Main control valve

(55) Fourth function control valve

(56) Auxiliary control valve

(57) Tilt control valve

(58) Lift control valve

(59) Line relief valve

(60) Line relief valve

(61) Stem

(62) Diverter valve

(63) Diverter valve

(64) Solenoid valve

(65) Solenoid valve

(66) Control group

(67) Lever (auxiliary)

(68) Lever (tilt)

(69) Lever (lift)




Illustration 14g00939695

Fourth Function

(54) Main control valve. (55) Fourth function control valve. (57) Tilt valve section. (62) Diverter valve. (63) Diverter valve. (64) Solenoid valve. (65) Solenoid valve.

If the machine is equipped with a fourth function, a fourth function control valve (55) will be installed. The movement of the stem in fourth function control valve (55) will be controlled by diverter valves (62, 63) and the travel of tilt lever (68).




Illustration 15g00939724

Dash Panel

(64) Solenoid valve. (65) Solenoid valve. (70) Control panel. (71) Fourth function switch.

In order to use the fourth function, fourth function switch (71) must be pushed forward. As the switch (71) is pushed forward, power is sent to solenoid valve (64) and to solenoid valve (65) in diverter valves (62) and (63). Solenoid valves (64, 65) will be energized.

Solenoid valves (64, 65) will divert the pilot oil flow from the tilt valve section to the fourth function control valve. Movement of the tilt lever on the pilot valve will send pilot oil to diverter valves (62) and (63). The pilot oil will be sent through diverter valve (62) and (63) to one of the pilot ports on fourth function control valve (55). The movement of the stem in fourth function control valve (55) will depend on the direction and the travel of the tilt lever.

The operation of the fourth function control valve is identical to the auxiliary valve section. For additional information about the operation of the fourth function control valve, refer to the Section "Auxiliary Control Valve".

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