312B Excavator Attachments Caterpillar

Boom Cylinder Drift

Refer to Testing and Adjusting, RENR1105 for information on testing the boom cylinder drift.

Manual Boom Lower Operation

1. Start the engine.

2. Fully extend the bucket cylinder (close bucket).

3. Fully retract the bucket cylinder (open bucket).

4. Raise the boom until the upper surface of the boom at the stick end becomes parallel to the ground. Stop the engine.

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Illustration 1	g00292938
(1) Cap (2) Locknut (3) Adjustment screw

5. Remove cap (1) .

6. Measure distance (A) .

7. Loosen locknut (2) of one boom lowering control valve.

8. Slowly turn adjustment screw (3) clockwise until the boom starts to lower.

   Note: The adjustment screw on either boom lowering control valve may be used in order to lower the boom. However, both adjustment screws may be used together in order to increase the speed of lowering.

   Note: The adjustment screw must be replaced after three uses.

9. When the front equipment has been completely lowered onto the ground, turn adjustment screw (3) counterclockwise until distance (A) is reached.

10. Tighten locknut (2) .

11. Replace cap (1) .

12. Before you put the machine into operation, make any necessary repairs.

For additional information, consult your Caterpillar dealer.

Relief Valves For Boom Cylinder Head End

Preparation

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Illustration 2	g00379772
(1) Tap (power shift pressure) (2) Tap (front pump delivery pressure)

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

2. Release the pressure in the hydraulic system. Refer to Testing And Adjusting, "Release of Pressure in the Hydraulic System" for information on releasing the hydraulic pressure.

3. Connect a 60000 kPa (8700 psi) pressure gauge to main pump pressure tap (2) .

4. Connect a 4000 kPa (580 psi) pressure gauge to tap (1) .

5. Start the engine and raise the hydraulic oil temperature to 55 ± 5°C (131 ± 9°F) .

6. Place the power mode selector switch in the POWER MODE position.

7. Place the engine speed dial at position 10 and maintain the maximum engine speed with no load on the engine. After the engine has been running for 3 seconds, check the engine speed.

   Note: The engine speed with no load should be 1980 ± 50 rpm.

8. Temporarily set the main relief valve pressure. Refer to Testing and Adjusting for information on temporarily setting the main relief valve pressure.

9. Start the "Service Mode" and keep the power shift pressure constant at 2450 kPa (355 psi) .

   Note: Normal operations of the engine and pumps is necessary for the pressure adjustment. If the pressure adjustments are not correct, check the characteristic curve for the engine and the pump. If the pump flow is lower than the specification, verify that there is no air in the hydraulic system. Refer to Testing And Adjusting, "Release of Air from Main Pumps" for information on releasing air from the main pump.

Test

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Illustration 3	g00379819

1. Fully extend the boom cylinders. Hold the implement control lever in the BOOM RAISE position.

2. Check the pressure at pressure tap (2) .

3. Fully extend the boom cylinders. Hold the implement control lever in the BOOM RAISE position.

4. Check the pressure at pressure tap (2) .

5. Reset the main relief valve pressure. Refer to Testing and Adjusting for information on setting the main relief valve pressure.

   Note: The relief valve is set to open at 31900 ± 1470 kPa (4625 ± 210 psi) .