302.5C Mini Hydraulic Excavator Hydraulic System Caterpillar

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Do not check for leaks with your hands. Pin hole (very small) leaks can result in a high velocity oil stream that will be invisible close to the hose. This oil can penetrate the skin and cause personal injury. Use cardboard or paper to locate pin hole leaks.

Testing Procedure

Note: The following tests require operating the engine at the HIGH IDLE position. Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)".

Illustration 1	g01187819
Main control valve (10) Main relief valve for the boom, bucket, and left travel control valves (P1) (11) Main relief valve for the stick, auxiliary, and right travel control valves (P2) (12) Main relief valve for the swing and blade control valves (P3)

1. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

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Illustration 2	g01187820
Main pump compartment (1) Pressure tap (P1) (2) Pressure tap (P2) (3) Pressure tap (P3) (4) Pressure tap (P4)

2. Open the door for the main pump compartment in order to access the pressure taps for the main relief valves.

3. Connect a 40000 kPa (5800 psi) pressure gauge to pressure tap (1) .

4. Connect a 40000 kPa (5800 psi) pressure gauge to pressure tap (2) .

5. Connect a 40000 kPa (5800 psi) pressure gauge to pressure tap (3) .

6. Start the engine.

7. Increase the engine speed lever to the HIGH IDLE position.

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

9. To check the main relief valve pressure setting at pressure tap (1) , move the joystick for the bucket until the bucket is at the full BUCKET CLOSE position (full extension of bucket cylinder). Hold the joystick for the bucket in this position.

10. Check the pressure on the pressure gauge at pressure tap (1) .

11. The pressure gauge reading should be 21700 ± 500 kPa (3147 ± 73 psi).

12. If the pressure is not within the specification, refer to "Adjustment (P1)" for the adjustment procedure.

13. To check the main relief valve pressure setting at pressure tap (2) , move the joystick for the stick until the stick is at the full STICK OUT position (full retraction of the stick cylinder). Hold the joystick for the stick in this position.

14. Check the pressure on the pressure gauge at pressure tap (2) .

15. The pressure gauge reading should be 21700 ± 500 kPa (3147 ± 73 psi).

16. If the pressure is not within the specification, refer to "Adjustment (P2)" for the adjustment procedure.

17. To check the main relief valve pressure setting at pressure tap (3) , move the lever for the blade until the blade is at the full BLADE UP position. Hold the lever for the blade in this position.

18. Check the pressure on the pressure gauge at pressure tap (3) .

19. The pressure gauge reading should be 18050 ± 450 kPa (2618 ± 65 psi).

20. If the pressure is not within the specification, refer to "Adjustment (P3)" for the adjustment procedure.

21. Return the engine speed lever to the LOW IDLE position.

22. Stop the engine.

Adjustment Procedure

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Illustration 3	g01187838

1. Open the cover on the right side of the machine in order to access the main control valve.

Adjustment (P1)

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Illustration 4	g01187863
Main control valve (10) Main relief valve (P1)

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Illustration 5	g01156988
Main relief valve (typical example) (13) Locknut (14) Adjustment screw

1. Loosen locknut (13) . Turn adjustment screw (14) clockwise in order to increase the pressure. Turn adjustment screw (14) counterclockwise in order to decrease the pressure. Tighten locknut (13) after the adjustment is made.

   Note: Always make final pressure adjustment on pressure rise.

Adjustment (P2)

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Illustration 6	g01187864
Main control valve (11) Main relief valve (P2)

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Illustration 7	g01156988
Main relief valve (typical example) (13) Locknut (14) Adjustment screw

1. Loosen locknut (13) . Turn adjustment screw (14) clockwise in order to increase the pressure. Turn adjustment screw (14) counterclockwise in order to decrease the pressure. Tighten locknut (13) after the adjustment is made.

   Note: Always make final pressure adjustment on pressure rise.

Adjustment (P3)

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Illustration 8	g01187867
Main control valve (12) Main relief valve (P3)

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Illustration 9	g01156988
Main relief valve (typical example) (13) Locknut (14) Adjustment screw

1. Loosen locknut (13) . Turn adjustment screw (14) clockwise in order to increase the pressure. Turn adjustment screw (14) counterclockwise in order to decrease the pressure. Tighten locknut (13) after the adjustment is made.

   Note: Always make final pressure adjustment on pressure rise.

Temporary Setting of the Main Relief Valves

Note: A temporary setting of the main relief valve is required before any line relief valve can be adjusted.

1. The temporary pressure value of the main relief valve should be 28950 ± 250 kPa (4200 ± 36 psi). If the main relief valves are not within the specification, adjust the main relief valve pressure setting to the correct pressure specification. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".

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Illustration 10	g01187819
Main control valve (10) Main relief valve for the boom, bucket, and left travel control valves (P1) (11) Main relief valve for the stick, auxiliary, and right travel control valves (P2) (12) Main relief valve for the swing and blade control valves (P3)

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Illustration 11	g01156988
Main relief valve (typical example) (13) Locknut (14) Adjustment screw

2. Loosen locknut (13) . Turn adjustment screw (14) clockwise for one half turn. Tighten locknut (13) after the adjustment is made.