824G Wheel Tractor, 825G Soil Compactor and 826G Landfill Compactor Hydraulic System Caterpillar

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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.

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Personal injury or death can result from machine articulation or movement. Machine frames can move and a person can be crushed. Connect the steering frame lock link between the front and rear frames before working on machine.

Reference: For the correct procedure to relieve any hydraulic oil pressure that may be in the steering system, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being tested.

Test the Pressure when the Engine Is Running

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Illustration 1	g00664484
The 825G Soil Compactor is shown.

1. Position the machine in the straight ahead position. Install the steering frame lock into the LOCKED position, as shown.

2. Engage the parking brake. Move the transmission direction control switch to the NEUTRAL position. Operate the engine at high idle. Move the implement control lever to the LIFT position in order to increase the temperature of the oil to normal operating temperature. Stop the engine.

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Illustration 2	g00664417

3. Install a 5000 kPa (725 psi) pressure gauge and hose assembly into the pressure tap for pilot oil. The pressure tap for pilot oil is located on the pilot control valve.

4. Start the engine. Run the machine at high idle. Record the pressure of the pilot oil. The correct pressure should be 3450 kPa (500 psi). Stop the engine.

5. Remove the pressure gauge and the hose, if the pressure is correct. The primary pressure reducing valve needs to be adjusted, if the pressure was not correct.

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Illustration 3	g00664511

6. The primary pressure reducing valve (3) is located on the pilot control valve. Loosen locknut (2). Turn adjusting screw (1) clockwise in order to increase the pressure of the pilot oil. Turn adjusting screw (1) counterclockwise in order to decrease the pressure of the pilot oil. Tighten the locknut.

7. Test the pressure of the pilot oil again. Adjust the pressure of the pilot oil, if necessary.

Test the Pressure when the Engine is Stopped

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Illustration 4	g00664484
The 825G Soil Compactor is shown.

1. Position the machine in the straight ahead position. Install the steering frame lock into the LOCKED position, as shown.

2. Engage the parking brake. Move the transmission direction control switch to the NEUTRAL position. Operate the engine at high idle. Move the implement control lever to the LIFT position in order to increase the temperature of the oil to normal operating temperature. Raise the blade to the maximum height. Stop the engine.

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Illustration 5	g00664417

3. Install a 5000 kPa (725 psi) pressure gauge and hose assembly into the pressure tap for pilot oil. The pressure tap for pilot oil is located on the pilot control valve.

4. Turn the ignition key to the ON position. The correct pressure on the pressure gauge should be 2070 kPa (300.2328 psi).

5. Remove the pressure gauge and the hose, if the pressure is correct. The secondary pressure reducing valve needs to be adjusted, if the pressure was not correct.

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Illustration 6	g00683760

6. The secondary pressure reducing valve (3) is located on the pilot control valve. Loosen locknut (2). Turn adjusting screw (1) clockwise in order to increase the pressure of the pilot oil. Turn adjusting screw (1) counterclockwise in order to decrease the pressure of the pilot oil. Tighten the locknut.

7. Test the pressure of the pilot oil again. Adjust the pressure of the pilot oil, if necessary.