992G Wheel Loader Electrohydraulic System Caterpillar

The line relief valve (dump) relieves pressure in the head end circuit of the tilt cylinder. This protects the components of the tilt circuit from damage. The line relief valve (dump) is set to a lower pressure setting than the main relief valve.

There are two bucket dump relief valves. One relief valve is in the main control valve for the left side and the other relief valve is in the main control valve for the right side. The two relief valves are connected to the head end circuit of the tilt cylinder. Therefore, the relief valve with the lowest setting will determine the pressure setting of the dump valve circuit.

A hydraulic test bench is the most accurate method for testing line relief valves. If it is not practical to use a test bench, then use this procedure in order to test the relief valves on the machine.

Reference: For the specifications of the line relief valve on a hydraulic test bench, refer to the Service Manual module Specifications, "Relief Valve (Line)" for the machine that is being serviced.

This procedure isolates the fixed displacement pump from the variable displacement pump. The fixed displacement pump supplies oil only to the left side of the implement control valve. The implement electronic control module (ECM) will activate only the left implement control valve during this check. All of the oil from the variable displacement pump flows through the deactivated right side of the implement control valve to the hydraulic tank.

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Illustration 1	g00287033
Manifold for Implement Hydraulics (1) Pressure tap for the fixed displacement pump.

1. Connect the steering frame lock link.

2. Attach a 5P-4816 Gauge (50000 kPa (7500 psi)) to pressure tap (1) on the manifold.

3. Engage the parking brake.

4. Shift the transmission to NEUTRAL position.

5. Start the engine. Warm the hydraulic oil to normal operating temperature of approximately 49 to 65°C (120 to 150°F).

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Illustration 2	g00287034
Right Console (2) Keypad.

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Illustration 3	g00287036
Front Dash (3) Diagnostic message screen.

6. Press the "OK" key on keypad (2) repeatedly. The hourmeter will appear on diagnostic message screen (3) .

7. On the keypad, enter "SERV" (the numbers 7378) and then press the "OK" key. Press the ">" key until the diagnostic message screen registers the following message:
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   Table 1

   "IMPL RLF - FIX PUMP"

8. Press the "OK" key. The following message will be displayed on the diagnostic message screen.
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   Table 2

   "IMPL RLF - FIX PUMP" "PRESS OK TO START"

9. Press the "OK" key. The following messages will be displayed on the diagnostic message screen:
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   Table 3

   "RLF PRES CHECK MODE" "IS TURNED ON"

   "LEFT VALVE ONLY" "WILL BE COMMANDED"

   "PROCEED W/ STANDARD" "SERVICE CHECKS"

   The following message will alternate with the previous message in five second intervals:

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   Table 4

   "PRESS" "<" "OR" ">" "TO SEE SPEC LIST"

   Note: The displayed specifications on the diagnostic message screen are the expected results for the test. The specifications in the service manual may not agree with the specifications on the diagnostic message screen. The service personnel should use the specifications that are displayed on the diagnostic message screen for testing. These specifications could be changed by future updates in the software for the implement ECM.

   Note: The following specifications are listed on the diagnostic message screen:

   • The setting for the main relief valve on the fixed displacement pump

   • The pressure setting for the dump line relief valves

   • The lift time for the bucket with the fixed displacement pump

   • The torque converter stall speed

   • The double stall speed for the fixed displacement pump

   • The setting for the left valve rack back line relief pressure

   • The setting for the left valve lower line relief pressure

   • The setting for the left valve raise line relief pressure

10. Run the engine speed at low idle.

11. Raise the bucket to a point that is approximately halfway between the ground and the full RAISE position.

12. Move the tilt control lever to the DUMP position in order to dump the bucket. Hold the tilt control lever in the DUMP position. Record the gauge reading.

13. Move the bucket to a level position. Lower the bucket to the ground.

14. Shut off the engine.

15. Use the specification from the "SPEC LIST" for the pressure setting of the relief valve. If the setting for the relief valve is correct proceed to Step 19. If the setting is not correct perform the following adjustment.

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Illustration 4	g00287041
Main Control Valve on Left Side (4) Line relief valve (dump). (5) Adjustment screw. (6) Locknut.

16. First, adjust the pressure in the line relief valve (dump) on the left side.
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    Table 5

    Pressure at Dump Line Relief Valve
    Turns	Pressure Change
    1/2	2930 kPa (425 psi)
    1/4	1450 kPa (210 psi)
    1/8	725 kPa (105 psi)

17. Loosen locknut (6). Turn adjustment screw (5) counterclockwise in order to decrease the pressure setting. Turn adjustment screw (5) clockwise in order to increase the pressure setting. Refer to Table 5 in order to determine the amount of rotation of the adjustment screw for the correct setting. Tighten locknut (6) .

    Note: When you adjust a relief valve, start the adjustment at a set point below the relief pressure. Adjust the pressure up to the specified pressure setting for the relief valve.

18. Repeat Steps 10 to 14 in order to measure the pressure at the new setting. Repeat Step 17 if further adjustment is required. Proceed to Step 19 if the pressure of the line relief valve is equal to the specification that is listed in the SPEC LIST. If you turn adjustment screw (5) clockwise and the pressure setting of the line relief valve does not increase, the line relief valve for the right control valve will need adjusting. Proceed to step 19. Once the line relief valve for the right control valve has been adjusted return to Step 10 of this procedure.

    Note: There are two line relief valves (dump). One relief valve is in the main control valve for the left side and the other relief valve is in the main control valve for the right side. The two relief valves are connected to the head end circuit of the tilt cylinder. Therefore, the relief valve with the lowest setting will determine the pressure setting of the dump valve circuit.

19. Perform adjustment of the line relief valve (dump) for the main control valve (right).

    Reference: For additional information about adjusting the line relief valve (dump) on the right side, Refer to Testing and Adjusting, "Relief Valve Pressure (Line, Tilt Cylinder Head End, Right Valve Dump)" for the machine that is being serviced.

20. Remove the pressure gauge from pressure tap (1) .

21. Remove the steering frame lock.