311B and 312B Excavators Hydraulic System Caterpillar

Note: Always adjust the travel operation of the main relief valve before adjustments are made to the implement operation of the main relief valve. An adjustment to the travel operation of the main relief valve will change the pressure setting of the implement operation of the main relief valve.

Travel Operation

Test

1. Position the machine on level ground and stop the engine.

2. Release the pressure in the hydraulic system. Refer to Testing And Adjusting, "Hydraulic System Pressure - Release".
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   Illustration 1	g00379594
   Pump compartment (1) Pressure tap (power shift pressure) (2) Pressure tap (rear pump delivery pressure) (3) Pressure tap (front pump delivery pressure)

3. Attach a 60000 kPa (8700 psi) pressure gauge to pressure tap (2).

4. Start the engine.

5. Place the machine controls at the following settings: Power Mode and engine speed dial "10".

6. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).
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   Illustration 2	g00380124
   (15) Sprocket (16) Stopper

7. Place stopper (16) in sprocket (15) in order to block forward left travel.

8. Slowly move the left travel control lever to full FORWARD position and check the pressure gauge reading at pressure tap (2).

9. Return the control lever to the NEUTRAL position.

Adjust

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Illustration 3	g00379596
(4) Adjustment screw (5) Locknut (6) Adjuster nut (7) Locknut (8) Main relief valve

1. Loosen locknut (7) and turn adjuster nut (6) until the pressure gauge reading at pressure tap (2) is 34300 ± 490 kPa (5000 ± 72 psi).

   Note: Turning adjuster nut (6) clockwise increases the pressure. Turning adjuster nut (6) counterclockwise decreases the pressure.

2. Tighten locknut (7) to a torque of 29 ± 2 N·m (22 ± 1 lb ft).

Note: Always make final pressure adjustments on pressure rise.

Implement Operation

Test

1. Position the machine on level ground and stop the engine.

2. Release the pressure in the hydraulic system. Refer to Testing And Adjusting, "Hydraulic System Pressure - Release".
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   Illustration 4	g00379594
   Pump compartment (1) Pressure tap (power shift pressure) (2) Pressure tap (rear pump delivery pressure) (3) Pressure tap (front pump delivery pressure)

3. Attach a 60000 kPa (8700 psi) pressure gauge to pressure tap (3).

4. Start the engine.

5. Place the machine controls at the following settings: Power Mode and engine speed dial "10".

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

7. Open the bucket until the bucket cylinder rod is at the full retraction. Check the pressure gauge reading at pressure tap (3).

8. Return the control lever to the NEUTRAL position.

Adjust

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Illustration 5	g00379596
(4) Adjustment screw (5) Locknut (6) Adjuster nut (7) Locknut (8) Main relief valve

1. Loosen locknut (5) and turn adjustment screw (4) until the pressure gauge reading at pressure tap (3) is 29900 ± 490 kPa (4350 ± 72 psi).

   Note: Turning adjustment screw (4) clockwise increases the pressure. Turning adjustment screw (4) counterclockwise decreases the pressure.

2. Tighten locknut (5) to a torque of 29 ± 2 N·m (22 ± 1 lb ft).

Note: Always make final pressure adjustments on pressure rise.