938H Wheel Loader and IT38H Integrated Toolcarrier Hydraulic System Caterpillar

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock.

Machine Preparation for Troubleshooting

1. Park the machine on a smooth, level surface. Move the machine away from other operating machines and away from personnel.

2. Permit only one operator on the machine. Keep all other personnel away from the machine or in the view of the operator.

3. Position the work tool on the ground.

4. Engage the parking brake.

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Illustration 1	g01402670

5. Place the steering frame lock in the LOCKED position.

Pilot Oil Accumulator

The following procedure can be used in order to test the pilot oil accumulator. The pilot oil accumulator maintains pressure in the pilot hydraulic system. The accumulator allows you to lower the boom, and the work tools with a stopped engine.

When you test or you charge the pilot oil accumulator, the pressure in the pilot hydraulic system must be released. The temperature of the nitrogen gas must also be taken into account. The pressure and volume of nitrogen gas varies with temperature.

Operational Test for the Pilot Oil Accumulator

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Illustration 2	g01402829
Right side of articulation joint (1) Pressure tap for pilot hydraulic system

1. Install an 8T-0850 Pressure Gauge from the 1U-5481 Pressure Gauge Group or a 198-4240 Digital Pressure Indicator to pressure tap (1) .

2. Start the engine and run the engine at HIGH idle. The pressure gauge will read 2620 ± 345 kPa (380 ± 50 psi).

3. Stop the engine. Turn the start switch to the ON position. Do not start the engine.

4. Move the implement control levers several times through the full range of travel. This will relieve any pressure that may be present in the implement hydraulic system. Turn the key start switch to the OFF position.

   Note: For more information on releasing the hydraulic system pressure, refer to Testing and Adjusting, "System Pressure - Release".

5. Watch the pressure gauge. Move the control lever or the joystick in order to lower the boom. The pressure will steadily decrease.

6. When the pressure is approximately 690 ± 34 kPa (100 ± 5 psi) the pressure will suddenly drop to zero. This occurs because no oil is left in the accumulator. The final pressure prior to the sudden drop to zero is the approximate pressure of the accumulator charge.

Discharging the Accumulator

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Illustration 3	g00384713

1. Ensure that the oil in the hydraulic system is at normal operating temperature. Park the machine on a smooth, level surface. Position the lift arms on the stands.

2. Install the steering frame lock. Block the wheels. Stop the engine.

3. With the engine stopped, turn the key start switch in the ON position. Move the implement control levers several times through the full range of travel. This will relieve any pressure that may be present in the implement hydraulic system. Turn the key start switch to the OFF position.

   Note: For more information on releasing the hydraulic system pressure, refer to Testing and Adjusting, "System Pressure - Release".

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Illustration 4	g01402881

4. Remove front guard (2) in order to access the pilot oil accumulator.

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Illustration 5	g01410268

5. Locate the pilot oil accumulator near the main control valve.

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Illustration 6	g01410294

6. Remove the protective cap which protects the charging valve of the accumulator.

7. Remove the protective cap on the nitrogen charging valve.

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Illustration 7	g00282185
(3) Nipple. (4) Coupling assembly. (5) Pressure gauge. (6) Hose assembly. (7) Coupling assembly. (8) Nipple. (9) Valve. (10) Pressure gauge. (11) Regulator assembly. (12) Pressure regulating screw. (13) Chuck for the nitrogen cylinder valve. (14) Valve handle. (15) Nitrogen charging chuck. (16) Hose assembly. (17) Tee.

8. Identify the correct nitrogen charging chuck.

   Note: For a nitrogen charging valve with a 0.305 inch -32 THD, use a 1S-8938 Nitrogen Charging Chuck and a 1U-5551 Extension Assembly. For a nitrogen charging valve with a 0.482 inch -26 THD, use a 7S-5106 Nitrogen Charging Chuck and a 7S-5439 Extension Assembly .

9. Attach hose assembly (16) to nitrogen charging chuck (15) .

10. Turn valve handle (14) on nitrogen charging chuck (15) all the way in the counterclockwise direction. This will ensure that the nitrogen charging valve will not be opened when nitrogen charging chuck (15) is attached to the nitrogen charging valve.

11. Attach nitrogen charging chuck (15) and hose assembly (16) to the nitrogen charging valve.

12. Place the open end of hose assembly (16) away from the work area and away from other personnel.

13. Turn valve handle (14) on nitrogen charging chuck (15) all the way in the clockwise direction in order to open the nitrogen charging valve. This will release all of the compressed gas from the accumulator through hose assembly (16). Now, the accumulator can be removed from the machine.

14. Disconnect the hydraulic lines for servicing, as needed.

Nitrogen Charging Procedure

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Illustration 8	g00107133
Nitrogen Charging Group (1) Nipple. (2) Coupling assembly. (3) Pressure gauge. (4) Hose assembly. (5) Coupling assembly. (6) Nipple. (7) Valve. (8) Pressure gauge. (9) Regulator assembly. (10) Pressure regulating screw. (11) Chuck for the nitrogen cylinder valve. (12) Valve handle. (13) Chuck. (14) Hose assembly.

1. Ensure that valve (7) is closed. Install chuck (13) onto the pilot oil accumulator. Turn valve handle (12) completely in the clockwise direction.

2. If the reading on pressure gauge (8) is too high, slowly open valve (7) in order to lower the pressure. If the reading on the pressure gauge is too low, use the following procedure to charge the accumulator:

   1. Connect a hose from the nitrogen cylinder to chuck (11) .

   2. Open the valve on the nitrogen cylinder. Adjust screw (10) on regulator assembly (9) until pressure gauge (3) is at the correct charging pressure.

   3. Slowly open valve (7) and charge the accumulator. Charge the accumulator to 690 ± 34 kPa (100 ± 5 psi) at a temperature of 21 °C (70 °F). Then, close valve (7). If pressure gauge (8) and pressure gauge (3) show the same reading and the readings do not change, the accumulator has the correct charge.

      If the pressure reading on gauge (8) decreases, open valve (7) and allow more nitrogen to fill the accumulator.

      Perform this procedure until pressure gauge (8) and pressure gauge (3) show the same reading. Make sure that neither reading changes when valve (7) is closed.

3. Close valve (7). Close the valve on the nitrogen cylinder.

4. Turn valve (12) on chuck (13) outward in the counterclockwise direction. Remove the test equipment.