302.5C Mini Hydraulic Excavator Hydraulic System Caterpillar


Relief Valve (Line) - Test and Adjust

Usage:

302.5C GBB

------ WARNING! ------

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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------ WARNING! ------

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.

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NOTICE

Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.

Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products.

Dispose of all fluids according to local regulations and mandates.


Testing Procedure

Table 1
Required Tools    
Part Number     Description     Qty    
8T-0860     Pressure Gauge     2    
6V-3014     Hose As     2    
6V-3989     Fitting     2    
6V-4143     Quick Connect Coupler     4    

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

Note: A temporary setting of the main relief valve is required before any line relief valve can be tested. Temporarily adjust main relief valve (P1) in order to test the boom line relief valves and the bucket line relief valve. Temporarily adjust main relief valve (P2) in order to test the stick line relief valves. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".

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



    Illustration 1g01187820

    Main pump compartment

    (1) Pressure tap (P1)

    (2) Pressure tap (P2)

    (3) Pressure tap (P3)

    (4) Pressure tap (P4)

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

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

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

  1. Start the engine.

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

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

  1. Move the joystick for the bucket to the BUCKET CLOSE position and hold.

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

  1. The pressure gauge reading should be 25250 ± 250 kPa (3662 ± 36 psi).

  1. Move the joystick for the boom to the BOOM LOWER position and hold.

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

  1. The pressure gauge reading should be 25250 ± 250 kPa (3662 ± 36 psi).

  1. Move the joystick for the stick to the STICK OUT position and hold.

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

  1. The pressure gauge reading should be 25250 ± 250 kPa (3662 ± 36 psi).

  1. Move the joystick for the stick to the STICK IN position and hold.

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

  1. The pressure gauge reading should be 25250 ± 250 kPa (3662 ± 36 psi).

  1. If any of the pressure readings are not set to the correct specifications, adjustment of that line relief valve is necessary. Refer to the "Adjustment Procedure".

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

  1. Stop the engine.

Adjustment Procedure




    Illustration 2g01187883

    Top view of main control valve

    (4) Line relief valve (bucket cylinder head end)

    (5) Line relief valve (boom cylinder rod end)

    (6) Line relief valve (boom cylinder head end)

    (7) Line relief valve (stick cylinder head end)

    (8) Line relief valve (stick cylinder rod end)

  1. The following line relief valves are located on the right side of the main control valve: (4) bucket cylinder head end, (6) boom cylinder head end and (7) stick cylinder head end. The following line relief valves are located on the left side of the main control valve: (5) boom cylinder rod end and (8) stick cylinder rod end.



    Illustration 3g01157045

    Line relief valve (typical example)

    (9) Locknut

    (10) Adjustment screw

  1. Determine the line relief valves that require adjustment. Loosen locknut (9). Turn adjustment screw (10) in order to adjust the pressure. Turning adjustment screw (10) clockwise increases the pressure. Turning adjustment screw (10) counterclockwise decreases the pressure. Tighten locknut (9) .

    Note: Always make final pressure adjustment on pressure rise.

    Note: Adjust the main relief valve to the specifications. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".

Caterpillar Information System:

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