MH3022, MH3024 and MH3026 Material Handlers Hydraulic System Caterpillar

Specification

Introduction

The main relief valve acts as a backup to the signal limiter valve. If the signal limiter valve fails and the control spools in the main control valve are returning to neutral, the main relief valve will open and limit the maximum main pump pressure.

Note: Prior to performing this test, the Testing and Adjusting, "Relief Valve (Pilot) - Test and Adjust" must be performed.

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 "1".

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	g03857098
    Signal pressure taps are located behind the left front access door

13. Connect tooling (B2) 60,000 kPa (8,702 psi) pressure sensor to main pump pressure tap.
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    Illustration 4	g03722485
    Service connector 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”.
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       NOTICE
       Creating main pump pressure higher than 38,000 kPa (5,512 psi) for more than five seconds may damage the machine.

    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. The pressure of the load sensing signal limiter valve for the main control valve is set to maximum and the pressure for the line relief valves are set 25,000 kPa (3,626 psi). Cat^® (ET) also allows the main pump pressure limit to be raised to provide high pressure of about 43,000 kPa (6,237 psi).

Temporary Setting of the Signal Limiter Relief Valve

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Illustration 5	g03729304
Main control valve (1) Main relief valve (2) Load sensing signal limiter valve (3) Adjustment screw (4) Locknut (5) Adjustment screw (6) Locknut

1. Loosen locknut (6) on load sensing signal limiter valve (2).

2. Turn adjustment screw (5) on load sensing signal limiter valve (2) clockwise by one half turn.

   Note: LS cutoff pressure should now be higher than the main relief valve pressure.

3. While the adjustment screw is being held, tighten the locknut on load sensing signal limiter valve (2) to the specified torque.

Test Procedure

1. Start the engine.

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

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

4. Push down on the power mode control button 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.
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   NOTICE
   If the blade and/or stabilizer are being used for the first time after new cylinder have been installed, switch off all blade and stabilizers, and stall in the OPEN position.

8. Stall one of the following circuits on the machine in the closed position to obtain a pressure reading:

   • Blade/Dozer Circuit

   • Stabilizer Circuit

   Note: These circuits are used because there are no line relief valves in these circuits.

9. Check the pressure at the main pump pressure tap. Refer to Table 1 for the correct pressure.

10. If the main pump pressure is not correct, refer to the "Adjustment Procedure".

Adjustment Procedure

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

1. Remove the cap from main relief valve (1).

2. Loosen the locknut on main relief valve (1).
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   NOTICE
   To avoid damage to the hydraulic components, do not turn the main relief valve adjustment screw into the stop.

3. Turn the adjustment screw for main relief valve (1) clockwise to increase the pressure. Turn the adjustment screw for main relief valve (1) counterclockwise to decrease the pressure.

   Note: A quarter turn of the adjustment screw will equal approximately 4,000 kPa (580 psi).

4. Check the pressure at the main pump pressure tap. Refer to Table 1 for the correct pressure.

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

5. While the adjustment screw on main relief valve (1) is being held, tighten the locknut to the specified torque.

6. Install the cap onto main relief valve (1).

7. Once the main relief pressure has been met, click the "Next" button to return to normal operation in Cat (ET).

8. Adjust load sensing signal limiter valve (2) to the correct pressure setting.

   Note: Refer to Testing and Adjusting, "Relief Valve (Signal Limiter) - Test and Adjust" in this manual for the adjustment procedure.