345 MHPUC Mobile Hydraulic Power Unit Hydraulic System Relief Valve (Pilot) - Test and Adjust Caterpillar


Relief Valve (Pilot) - Test and Adjust
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345 MHPUC Mobile Hydraulic Power Unit Hydraulic System [KENR7932]

Note: Certain machines will default to "Economy Mode" at machine startup. Change to "High Hydraulic Power Mode" before performing the test procedure.

  1. Place the machine on level ground.

  2. Stop the engine.

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


    Illustration 1g01127957
    Pilot oil manifold compartment
    (28) Locknut
    (29) Setscrew
    (30) Pressure tap
    (31) Pilot filter

  4. Connect a 6000 kPa (870 psi) pressure gauge to pressure tap (30).

  5. Start the engine.

  6. Place the machine controls at the following settings: engine speed dial "10" and AEC switch OFF. Refer to Testing and Adjusting, "Engine Performance - Test (Engine Speed)" for engine rpm settings.

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

  8. Check the pilot relief valve setting at pressure tap (30).

  9. The pilot relief valve setting should be 4100 ± 200 kPa (595 ± 30 psi). If the pilot relief valve setting is not within the specification, adjust the pilot relief valve.

  10. In order to adjust the pilot relief valve, loosen locknut (28).

  11. Turn setscrew (29) until the pressure gauge reading at pressure tap (30) is 4100 ± 200 kPa (595 ± 30 psi).

    Note: Turning setscrew (29) clockwise increases the pressure. Turning setscrew (29) counterclockwise decreases the pressure.

    Note: Always make final pressure adjustments on pressure rise.

  12. Tighten locknut (28) to a torque of 49 ± 4.9 N·m (36 ± 4 lb ft).

Note: Normal operation of the engine and pumps are necessary for the pressure adjustment. If the results of the pressure adjustments are not correct, then the engine and the pump characteristic curve needs to be checked.

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