321C CR Excavator Hydraulic System Caterpillar

1. Position the machine on level ground and stop the engine.

2. Release the pressure in the hydraulic system. Refer to Testing And Adjusting, "Hydraulic System Pressure - Release".

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Illustration 1	g00952442
Pump compartment (1) Pressure tap (delivery pressure of the drive pump) (2) Pressure tap (delivery pressure of the idler pump) (3) Pressure tap (power shift pressure)

3. Attach a 60000 kPa (8700 psi) pressure gauge to pressure tap (1) .

4. Start the engine.

5. Place the machine controls at the following settings: engine speed dial "10" and AEC switch OFF. Refer to Testing and Adjusting, "Engine Performance - Test" for engine rpm settings.

6. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).

7. Open the bucket until the bucket cylinder rod is at the full retraction.

8. Check the main relief valve pressure setting at pressure tap (1) .

9. Return the joystick for the bucket to the NEUTRAL position.

10. The main relief valve pressure setting should be 34300 ± 490 kPa (4950 ± 72 psi). If the main relief valve pressure setting is not within the specification, adjust the main relief valve pressure setting.

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Illustration 2	g00952443
Top of the main control valve (4) Adjustment screw (5) Locknut (6) Main relief valve

11. In order to adjust the main relief valve, loosen locknut (5) and turn adjustment screw (4) until the pressure gauge reading at pressure tap (1) is 34300 ± 490 kPa (4950 ± 72 psi).

    Note: Turning adjustment screw (4) clockwise increases the pressure. Turning adjustment screw (4) counterclockwise decreases the pressure.

    Note: Always make final pressure adjustments on pressure rise.

12. Tighten locknut (5) to a torque of 50 ± 10 N·m (37 ± 7 lb ft).

Temporary Setting of the Main Relief Valve

Note: A temporary setting of the main relief valve is required before any line relief valve can be adjusted.

1. The main relief valve pressure setting should be 34300 ± 490 kPa (4950 ± 72 psi). If the main relief valve is not within the specification, adjust the main relief valve pressure setting to the correct pressure specification before performing Step 2. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".

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Illustration 3	g00952443
Top of the main control valve (4) Adjustment screw (5) Locknut (6) Main relief valve

2. Loosen locknut (5) and turn adjustment screw (4) clockwise for one half turn. Tighten locknut (5) to the specified torque.

   Note: Always make final pressure adjustments on pressure rise.