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

Introduction

The crossover relief valves are located on the travel counterbalance valves. The following procedure will determine if the crossover relief valves are out of adjustment.

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	g02173315
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) or pressure tap (2) .

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Illustration 2	g02173314
(3) FT-2542 Blocker Pin (4) Sprocket

5. Place blocker pin (3) in sprocket (4) in order to block forward left travel.

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Illustration 3	g02175922
Signal relief valve for low pressure (travel circuit)

6. Increase the setting of the low-pressure signal relief valve. Turn the adjustment screw clockwise on the signal relief valve for ONE turn. Refer to Testing and Adjusting, "Relief Valve (Signal) - Test and Adjust" for additional information on the temporary setting of the signal relief valve.

Test Procedure

1. Start the engine.

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Illustration 4	g02173316
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 "10"

   • AEC switch OFF

   • Gain/Response "AVS" (normal mode)

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

3. Place the hydraulic activation control lever in the UNLOCKED position.

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

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Illustration 5	g02173313
Travel motor (left side) (5) Crossover relief valve (forward left travel) (6) Crossover relief valve (reverse left travel) (7) Adjustment screw (8) Locknut

5. Slowly move the left travel control lever to full FORWARD position and check the pressure reading at pressure tap (1) or (2). The pressure setting of crossover relief valve (5) should be 39250 + 1500 - 2000 kPa (5693 + 218 - 290 psi).

6. Return the left travel control lever to the NEUTRAL position.

7. In order to adjust crossover relief valve (5), loosen locknut (8) and turn adjustment screw (7) until the pressure reading at pressure tap (1) or (2) is 39250 + 1500 - 2000 kPa (5693 + 218 - 290 psi).

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

   Note: Always make final pressure adjustment on pressure rise.

8. Tighten locknut (8) to a torque of 155 ± 29 N·m (115 ± 22 lb ft).

9. Place blocker pin (3) in sprocket (4) in order to block reverse left travel.

10. Slowly move the left travel control lever to full REVERSE position and check the pressure reading at pressure tap (1) or (2). The pressure setting of crossover relief valve (6) should be 39250 + 1500 - 2000 kPa (5693 + 218 - 290 psi).

11. Return the left travel control lever to the NEUTRAL position.

12. In order to adjust crossover relief valve (6), loosen locknut (8) and turn adjustment screw (7) until the pressure reading at pressure tap (1) or (2) is 39250 + 1500 - 2000 kPa (5693 + 218 - 290 psi).

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

    Note: Always make the final pressure adjustment on pressure rise.

13. Tighten locknut (8) to a torque of 155 ± 29 N·m (115 ± 22 lb ft).

14. Return the signal relief valve for the travel circuit to the specified pressure setting after the pressure settings for the travel crossover relief valves are attained. Refer to Testing and Adjusting, "Relief Valve (Signal) - Test and Adjust".

In order to adjust the crossover relief valves on the right travel motor, place blocker pin (3) in the sprocket for the right travel motor. Adjust the crossover relief valves on the right travel motor in the same manner as the adjustment for the left travel motor.