M318F, M320F and M322F Wheeled Excavators Hydraulic System Caterpillar

Specification

Introduction

The unloading valve prevents the hydraulic system from margin pressure spikes. This procedure verifies that the unloading valve is function properly.

Required Tools

Illustration 1	g02726620

Machine Preparation

1. Clear all personnel from the machine and from the area around the machine.

2. Start the engine.
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   Illustration 2	g02449876
   Engine speed dial

3. Set the engine speed dial at "10".

4. Lower the left console.

5. Position the machine on level ground. Check the visibility and adjust the mirrors for the best vision close to the machine.

6. Fully depress the service brake pedal until the service brake pedal locks mechanically.

7. Increase the hydraulic oil temperature to 46° to 60° C (115° to 140° F).

8. Lower the stabilizers and the blade tip.

9. Fully extend the bucket cylinder and place the bucket on the ground.

10. Stop the engine.

11. Release the pressure in the hydraulic system.

    Note: Refer to Testing and Adjusting, "System Pressure - Release".

12. Raise the left console.
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    Illustration 3	g03730576
    Signal pressure taps are located behind the left rear access door (1) Main pump pressure tap (2) Load sensing signal pressure tap

13. Connect tooling (B2) 60,000 kPa (8,702 psi) pressure sensor to main pump pressure tap (1). Connect tooling (B2) 60,000 kPa (8,702 psi) pressure sensor to load sensing signal pressure tap (2).
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    Illustration 4	g03722485
    Service connector located on the right side of cab behind the seat

14. Connect tooling (E) to the service connector.

    1. Start the Electronic Technician.

    2. Select the Machine ECM and then select “OK”.

    3. Select “Service” from the main menu.

    4. Select “Service Procedures”.

    5. Select "Line and Main Relief Adjustments".

       Note: This selection provides a permanent flow of about 40 L/min (11 US gpm) from the main pump without any margin pressure control.

Check Procedure

1. Start the engine.
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   Illustration 5	g02452604
   Engine speed dial

2. Set the engine speed dial at "1".

3. Lower the left console.
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   Illustration 6	g02446738
   Power mode control button located on the soft panel switch

4. Push down on the power mode control button in order to activate power mode.

   Note: The indicator light will be illuminated when power mode is activated.

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   Illustration 7	g02447036
   Automatic Engine Speed Control (AESC) as displayed on the programmable function key in the monitor.

5. Disable the automatic engine speed control through the monitor by pressing the programmable button.
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   Illustration 8	g03722432
   Hydraulic modulation switch on left joystick

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   Illustration 9	g06174873
   Hydraulic modulation medium mode (monitor display)

6. Select the hydraulic modulation mode as medium. Press the lower front switch on the left joystick to select the hydraulic modulation mode.

7. The air conditioning should be turned off for the following test.

8. Check margin pressure.

   Note: Margin pressure is equal to main pump pressure (1) minus load sensing signal pressure (2).