924K, 930K and 938K Wheel Loaders Electrohydraulic System Caterpillar

Reference: Refer to Testing and Adjusting, "Machine Preparation for Troubleshooting" for the machine that is being serviced.

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

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Personal injury or death can result from escaping fluid under pressure. Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

Specifications

Required Tools

Introduction

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 lift arms with the engine stopped.

Test

Illustration 1	g02793883
Pilot Oil Accumulator

The pilot oil accumulator is located under the access panel on the front of the machine.

The following conditions must be met before the hydraulics will operate:

• The key must be on.

• The "Hydraulic Lockout" switch on the console must be in the ENABLED position.

1. Start the engine.

2. Ensure that the oil in the hydraulic system is at normal operating temperature.

3. Raise the lift arms.

4. Ensure that the Hydraulic Lockout switch is in the ENABLED position. Shut off the engine.

5. Turn the key to the ON position.

6. Activate the control to lower the worktool.

7. The worktool should lower to the ground if the accumulator is charged.

Charge

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Dry nitrogen is the only gas approved for use in the accumulators. The charging of oxygen gas in an accumulator will cause an explosion. An explosion can be eliminated by using nitrogen gas cylinders with standard CGA (Compressed Gas Association, Inc.) No. 580 connectors. When nitrogen gas is ordered, make sure to order the cylinders with CGA No. 580 connectors. Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application, never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity).

A new accumulator should be charged before installation. Do not charge an accumulator that is connected to a hydraulic system. Pressure from the hydraulic oil in the system may interfere with the charging procedure.

Gas pressure is variable with the temperature. The accumulator must be at the same temperature as the surrounding air before the accumulator can be charged. Use the following chart for the correct nitrogen charge. Use dry nitrogen.

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Illustration 2	g00281220
Nitrogen charging apparatus (1) Pressure gauge (2) Connection to nitrogen cylinder valve (3) Regulator assembly (4) Valve (5) Pressure gauge (6) Pressure regulating screw (7) Valve handle (8) Chuck

1. Connect the nitrogen charging apparatus to the nitrogen cylinder at fitting (2).

2. Open the valve on the nitrogen cylinder.

3. Close valve (4).
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   Illustration 3	g02793926

4. Remove the cap from valve (9) of accumulator (10).

5. Install chuck (8) on valve (9) of the accumulator. Open valve handle (7) on chuck (8). Use gauge (5) to monitor the nitrogen charge in the accumulator.

6. Check the temperature of the air around the accumulator. Refer to Table 3 for the correct charging pressure.

7. Open the valve on the nitrogen cylinder. Adjust screw (6) on the regulator assembly until gauge (1) is at the pressure that will charge the accumulator.

8. When the pressures on gauge (5) and on gauge (1) are identical, turn off valve (4).

9. If the pressure on gauge (5) decreases, open valve (4).

10. Repeat Steps 8 and 9 until you have the following results:

    • Pressure readings on gauge (5) and on gauge (1) are identical.

    • Pressure readings do not change.

11. Close the valve on the nitrogen cylinder.

12. Close valve handle (7) on chuck (8).

13. Remove chuck (8) from valve (9) of the accumulator. Install the cap on valve (9) of the accumulator.

14. Install the pilot oil accumulator onto the machine.

15. Proceed to the “Test” section.