390D Excavator Hydraulic System Relief Valve (Pilot) - Test and Adjust 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	g02175588
   Lower compartment under the main control valve (1) Pressure tap (2) Pilot manifold (3) Adjustment screw (4) Locknut

3. Connect a 34,450 kPa (5,000 psi) pressure sensor to pressure tap (1).

4. Start the engine.
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   Illustration 2	g02175587
   Monitor and keypad (A) Engine speed (B) Gain/Response (C) AEC switch (D) Gain/Response switch

5. Place the machine controls at the following settings:

   • Engine speed dial "10"

   • AEC switch OFF

   • Gain/Response "AVS" (normal mode)

   Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.

6. Place the hydraulic lockout lever in the UNLOCKED position.

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

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

9. The pilot relief valve setting should be 4120 ± 100 kPa (600 ± 15 psi). If the pilot relief valve setting is not within the specification, adjust the pilot relief valve.

10. In order to adjust the pilot relief valve, loosen locknut (4).

11. Turn adjustment screw (3) until the pressure gauge reading at pressure tap (1) is 4120 ± 100 kPa (600 ± 15 psi).

    Note: A full turn of the adjustment screw changes the pressure by approximately 690 kPa (100 psi). Turning adjustment screw (3) clockwise increases the pressure. Turning adjustment screw (3) counterclockwise decreases the pressure.

    Note: Always make final pressure adjustments on pressure rise.

12. Tighten locknut (4) to a torque of 16 ± 1 N·m (12 ± 1 lb ft).

Note: Normal operation of the engine and pumps are necessary for the pressure adjustment. If the results of the pressure adjustments are not correct, then check the engine and the pump characteristic curve.