349D2 MHPU Mobile Hydraulic Power Unit Hydraulic System Relief Valve (Line) - Test and Adjust Caterpillar

Specification

Note: Certain machines will default to "Economy Mode" at machine startup. Change to "High Hydraulic Power Mode" before performing the test procedure.

Introduction

The line relief valves are located between each cylinder and the respective control valve. The line relief valve limits the overload pressures that can be created in the implement cylinders. The line relief valves are accessible from above the main control valve and below the machine after removal of the access plate.

Machines not equipped with front-end implements may still perform this test at the main control valve to check the line relief pressures.

Required Tools

Illustration 1	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

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, "Hydraulic System Pressure - Release".
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   Illustration 2	g03409582
   Pump compartment (1) Pressure tap (drive pump pressure) (2) Pressure tap (idler pump pressure)

4. Attach both 41,368 kPa (6,000 psi) pressure sensors to pressure tap (1) and pressure tap (2).

Test Procedure

Note: A temporary setting of the main relief valve is required before any line relief valves can be adjusted. Refer to Table 3 for temporary main relief setting for the function being tested.

Note: Pressure values in Table 4 are approximate values. Use a pressure gauge for adjustment.

Boom Cylinder Rod End, Stick Cylinder Rod End, and Stick Cylinder Head End

Note: A continuous relief of the valve for more than 10 seconds is not allowed.

Illustration 3	g06014198
Main control valves (front view) (4) Line relief valve (stick cylinder rod end) (5) Line relief valve (boom cylinder rod end) (6) Line relief valve (stick cylinder head end)

1. Start the engine.

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

3. Place the machine controls at the following settings: engine speed dial "10" and AEC switch OFF. Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.

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

5. Move the joystick for the stick until the stick is at the full STICK OUT position (full retraction of the stick cylinder).

6. Check the main relief valve pressure setting at pressure tap (1) or pressure tap (2). The main relief valve pressure setting should be 35000 + 500 — 1000 kPa (5076 + 73 — 145 psi).
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   Illustration 4	g02102305
   Main relief valve (standard) (A) Adjustment screw (L) Locknut

7. Loosen the locknut. Set the main relief pressure to 32800 kPa (4757 psi). Tighten the locknut.

   Note: Turn the adjustment screw clockwise to increase the pressure. Turn the adjustment screw counterclockwise to decrease the pressure.

   Note: Always make final pressure adjustments on pressure rise.

8. Verify the temporary main relief pressure setting with a second function. Move the joystick for the boom until the boom is at full BOOM RAISE position (full extension of the boom cylinder). The main relief pressure should be 32800 kPa (4757 psi).

9. Mark the original position of the line relief for the stick cylinder head end (6).

10. Move the joystick for the stick until the stick cylinder is at the full STICK IN position (full extension of stick cylinders).

11. Check the pressure setting of the line relief for the stick cylinder head end (6).

12. Loosen the locknut of the stick line relief valve. Turn adjustment screw of the stick line relief valve until the pressure reading at pressure tap (1) is 32800 kPa (4757 psi).

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

    Note: To prevent over setting, the adjustment should be stopped immediately after the pressure becomes within specification.

13. Repeat Step 9 to Step 12 for the following line relief valves:

    • Line relief valve for stick cylinder rod end

    • Line relief valve for boom cylinder rod end

14. Reset main relief valve pressure setting to the normal operating condition after the completion of the line relief test and adjust. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".