MH3022, MH3024 and MH3026 Material Handlers Hydraulic System Caterpillar

Specification

Introduction

The load sensing signal ensures that the main pump pressure does not overload the engine below full load rpm. The load sensing signal works with the margin stem to control the pump displacement. As system pressure rises, the load sensing signal will cause the main pump to destroke. Destroking the main pump ensures that a constant load is placed on the engine.

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

Required Tools

Illustration 1	g01623868
Tooling (B) 198-4240 Digital Pressure Indicator Gp

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	g03857086
    Signal pressure taps are located behind the left front access door

13. Connect tooling (B2) 41,368 kPa (6,000 psi) pressure sensor to the load sensing signal pressure tap.

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

Test Procedure

1. Start the engine.

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

3. Lower the left console.
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   Illustration 4	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 5	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 6	g03722432
   Hydraulic modulation switch on left joystick

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   Illustration 7	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. Slowly move an implement (boom, bucket, stick) to the full CLOSE position or the full OPEN position and hold.

9. Check the pressure at the load sensing signal pressure at pressure tap.

   Note: Refer to Table 1 in this manual for the correct pressure.

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   Illustration 8	g03728759
   Joystick (right button)

10. Enable heavy lift mode, if equipped. Press the top right button on the right joystick to activate heavy lift mode.

    Note: The indicator for heavy lift mode will illuminate on the monitor when heavy lift mode is active.

    Note: The heavy lift mode is only active for 60 seconds after the top right button on the right joystick is pressed.

11. Slowly move an implement (boom, bucket, stick) to the full CLOSE position or the full OPEN position and hold.

12. Check the pressure at the load sensing signal pressure at pressure tap.

    Note: Refer to Table 1 in this manual for the correct pressure.

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

14. Stop the engine.

15. Release the pressure in the hydraulic system.

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

16. Raise the left console.

17. If the load sensing signal pressure is not correct, refer to the "Adjustment Procedure".

Adjustment Procedure

1. To adjust the load sensing signal pressure, slowly move the bucket control lever to the full BUCKET CLOSE position and hold.
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   Illustration 9	g03728768
   Main control valve (typical example) (1) Adjustment screw (2) Locknut (3) Adjustment screw (4) Locknut (5) Load sensing signal limiter valve

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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.

2. Loosen locknut (2) on load sensing signal limiter valve (5).

3. Turn adjustment screw (1) into the stop on load sensing signal limiter valve (5).

4. Loosen locknut (4) on load sensing signal limiter valve (5).

5. Turn adjustment screw (3) on load sensing signal limiter valve (5) until the pressure for heavy lift is set.

   Note: A quarter turn of the adjustment screw clockwise increases the pressure by approximately 7,000 kPa (1,015 psi).

6. While adjustment screw (3) on load sensing signal limiter valve (5) is being held, tighten locknut (4).

7. Turn adjustment screw (1) on load sensing signal limiter valve (5) until the cutoff pressure is set to the correct specification. Refer to Table 1 for the correct "Standard load sensing signal pressure".

   Note: A quarter turn of the adjustment screw clockwise increases the pressure by approximately 6,000 kPa (875 psi).

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

8. While adjustment screw (1) on load sensing signal limiter valve (5) is being held, tighten locknut (2).

9. Repeat the "Test Procedure" until the load sensing pressure from Table 1 has been met.