305 CR Mini Hydraulic Excavator Hydraulic System Relief Valve (Main) - Test and Adjust Caterpillar


Relief Valve (Main) - Test and Adjust
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1.1. Testing Procedure
2.1. Adjustment Procedure
3.2. Adjustment (P1)
4.2. Adjustment (P2)
5.2. Adjustment (P3)
6.1. Temporary Setting of the Main Relief Valves

------ 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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Testing Procedure

Table 1
Required Tools    
Part Number     Description     Quantity    
8T-0860     Pressure Gauge     3    
6V-3014     Hose     3    
6V-4143     Coupler Assembly     6    

Before you perform these procedures, refer to Testing and Adjusting, "Machine Preparation" for the proper procedure to prepare the machine.

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




Illustration 1g00836916

Main control valve

(P1) Main relief valve for the boom, bucket, and left travel control valves

(P2) Main relief valve for the stick, auxiliary, and right travel control valves

(P3) Main relief valve for the boom swing, swing, and blade control valves

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



    Illustration 2g00836560

    Engine compartment

    (1) Pressure tap (P1)

    (2) Pressure tap (P2)

    (3) Pressure tap (P3)

  1. Open the engine hood 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. Connect a 40000 kPa (5800 psi) pressure gauge to pressure tap (3) .

  1. Start the engine. Increase the engine speed to high idle.

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

  1. 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.

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

  1. The pressure should be 24500 +1500/(-0) kPa (3553 +218/(-0) psi).

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

  1. 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.

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

  1. The pressure should be 24500 +1500/(-0) kPa (3553 +218/(-0) psi).

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

  1. To check the main relief valve pressure setting at pressure tap (3), move the boom swing control to the SWING LEFT position and hold. Make a note of the reading on the gauge attached to pressure tap (3) .

  1. The pressure should be 24500 +1500/(-0) kPa (3553 +218/(-0) psi).

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

  1. Return the engine to low idle. Stop the engine.

Adjustment Procedure




    Illustration 3g00816610

  1. Remove rubber cover (4) from the travel speed switch.

  1. Remove floormat (5) .



    Illustration 4g00836834

  1. Remove the bolts and the washers from floorplate (6) .



    Illustration 5g00836837

  1. Lift floorplate (6) in order to access electrical connector (7) .

  1. Disconnect electrical connector (7) to the travel speed switch.

  1. Remove floorplate (6) from the cab.



    Illustration 6g00836843

  1. Remove cover (8) from the machine.

Adjustment (P1)




    Illustration 7g00836845

    Main control valve

    (9) Main relief valve (P1)




    Illustration 8g00836893

    Main relief valve (typical example)

    (12) Locknut

    (13) Adjustment screw

  1. Loosen locknut (12). Turn adjustment screw (13) clockwise in order to increase the pressure. Turnadjustment screw (13) counterclockwise in order to decrease the pressure. Tighten locknut (12) after the adjustment is made.

    Note: Always make final pressure adjustment on pressure rise.

Adjustment (P2)




    Illustration 9g00836879

    Main control valve

    (10) Main relief valve (P2)




    Illustration 10g00836893

    Main relief valve (typical example)

    (12) Locknut

    (13) Adjustment screw

  1. Loosen locknut (12). Turn adjustment screw (13) clockwise in order to increase the pressure. Turnadjustment screw (13) counterclockwise in order to decrease the pressure. Tighten locknut (12) after the adjustment is made.

    Note: Always make final pressure adjustment on pressure rise.

Adjustment (P3)




    Illustration 11g00836901

    Main control valve

    (11) Main relief valve (P3)




    Illustration 12g00836893

    Main relief valve (typical example)

    (12) Locknut

    (13) Adjustment screw

  1. Loosen locknut (12). Turn adjustment screw (13) clockwise in order to increase the pressure. Turnadjustment screw (13) counterclockwise in order to decrease the pressure. Tighten locknut (12) 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 main relief valve pressure settings should be 24500 +1500/(-0) kPa (3553 +218/(-0) psi). If the main relief valves are not within the specification, adjust the main relief valve pressure setting to the correct pressure specification before performing the temporary setting. Refer to Testing and Adjusting, "Relief Valve (Main) - Test and Adjust".



    Illustration 13g00836916

    Main control valve

    (P1) Main relief valve for the boom, bucket, and left travel control valves

    (P2) Main relief valve for the stick, auxiliary, and right travel control valves

    (P3) Main relief valve for the boom swing, swing, and blade control valves




    Illustration 14g00836893

    Main relief valve (typical example)

    (12) Locknut

    (13) Adjustment screw

  1. Loosen locknut (12). Turn adjustment screw (13) clockwise for one half turn. Tighten locknut (12) after the adjustment is made.

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