374D Excavator Hydraulic System Relief Valve (Counterweight Cylinder) - Test and Adjust Caterpillar

Introduction

The line relief valve is located between the cylinder and the respective control valve. The line relief valve limits the overload pressures that can be created in the cylinder. The line relief valve and the controls for the counterweight removal system is located in the pump compartment.

Required Tools

Machine Preparation

1. Position the machine on level ground.

2. Stop the engine.

3. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release".

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Illustration 1	g02173377
Main pumps (left side view) (1) Pressure tap (front pump delivery pressure) (2) Pressure tap (rear pump delivery pressure)

4. Connect a 41,368 kPa (6,000 psi) pressure sensor to pressure tap (1) .

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Illustration 2	g00748970
Upper left view of pump compartment (3) Switch (4) Control lever (5) Ball valves (A) CLOSED position (B) OPEN position

5. Place switch (3) in the UP position.

6. Place ball valves (5) in the OPEN position (B) .

Test and Adjust Procedure

1. Start the engine.

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Illustration 3	g02173378
Monitor and keypad (A) Engine speed (B) Gain/Response (C) AEC switch (D) Gain/Response switch

2. Place the machine controls at the following settings:
   • Engine speed dial "2"

   • AEC switch OFF

   • Gain/Response "AVS" (normal mode)

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

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

4. Move control lever (4) upward and read the relief valve pressure setting at pressure tap (1). The relief valve pressure setting should be 20600 +1000 - 0 kPa (2990 + 145 - 0 psi).

5. Return control lever (4) back to the NEUTRAL position.

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Illustration 4	g00748950
(6) Locknut (7) Adjustment screw

6. To adjust the relief valve pressure setting, loosen locknut (6) and turn adjustment screw (7) until the pressure reading at pressure tap (1) is 20600 +1000 - 0 kPa (2990 + 145 - 0 psi).

   Note: Turning adjustment screw (7) clockwise increases the pressure. Turning adjustment screw (7) counterclockwise decreases the pressure.

7. Tighten locknut (6) to a torque of 30 ± 2 N·m (22 ± 1 lb ft).

   Note: Always make final pressure adjustments on pressure rise.

8. Return switch (3) to the DOWN position. Return ball valves (5) to the CLOSED position (A) .