308C CR Excavator Hydraulic System – Relief Valve (Blade) – Test and Adjust – If Equipped

Blade Main Relief Valve

  1. Position the machine on level ground.
  1. Stop the engine.
  1. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, “Hydraulic System Pressure – Release”.



    Illustration 1 g00858378

    (1) Blade pump

    (2) Pressure tap (delivery pressure for the blade pump)

  1. Connect a 60000 kPa (8700 psi) pressure gauge to pressure tap (2) .
  1. Start the engine.
  1. Place the machine controls at the following settings: engine speed dial “10” and Low idle switch OFF. Refer to Testing and Adjusting, “Engine Performance – Test” for engine rpm settings.
  1. Place the hydraulic activation control lever in the UNLOCKED position.
  1. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).
  1. Slowly move the blade control lever to the full RAISE position and check the pressure gauge reading at pressure tap (2). The pressure setting should be 20600 ± 1470 kPa (3000 ± 215 psi).
  1. Return the blade control lever to the NEUTRAL position.



    Illustration 2 g00858382

    Blade control valve

    (3) Locknut

    (4) Blade main relief valve

    (5) Adjustment screw

    (6) Adjustment screw

    (7) Blade line relief valve

    (8) Locknut

  1. In order to adjust blade main relief valve (4), loosen locknut (8) and turn adjustment screw (6) until the pressure gauge reading at pressure tap (2) is 20600 ± 1470 kPa (3000 ± 215 psi).

    Note: Turning adjustment screw (6) clockwise increases the pressure. Turning adjustment screw (6) counterclockwise decreases the pressure.

    Note: Always make final pressure adjustment on pressure rise.

  1. Tighten locknut (8) to a torque of 29 ± 2 N·m (21 ± 1 lb ft).

Blade Line Relief Valve

Note: A temporary setting of the blade main relief valve is required before the blade line relief valve is adjusted.




    Illustration 3 g00858378

    (1) Blade pump

    (2) Pressure tap (delivery pressure for the blade pump)

  1. Connect a 60000 kPa (8700 psi) pressure gauge to pressure tap (2) .
  1. Perform the following steps in order to make a temporary adjustment to the blade main relief valve.
    1. Move the blade control lever until the blade is at the full RAISE position (full retraction of the blade cylinder). Hold the blade control lever in this position.
    1. Check the pressure setting of the blade main relief valve at pressure tap (2) .
    1. Return the blade control lever to the NEUTRAL position.



      Illustration 4 g00858382

      Blade control valve

      (3) Locknut

      (4) Blade main relief valve

      (5) Adjustment screw

      (6) Adjustment screw

      (7) Blade line relief valve

      (8) Locknut

    1. Loosen locknut (8) on blade main relief valve (4). Turn adjustment screw (6) until the pressure gauge reading at pressure tap (2) is 27500 kPa (4000 psi).

      Note: Turn adjustment screw (6) clockwise in order to increase the pressure. Turn adjustment screw (6) counterclockwise in order to decrease the pressure.

    1. Tighten locknut (8) to a torque of 29 ± 2 N·m (21 ± 1 lb ft).
  1. To adjust the pressure setting of the blade line relief valve, move the blade control lever to the full LOWER position (full extension of the blade cylinder). Hold the blade control lever in this position.
  1. Check the line relief valve pressure setting of the blade cylinder at pressure tap (2) .
  1. Return the blade control lever to the NEUTRAL position.
  1. Loosen locknut (3) on blade line relief valve (7). Turn adjustment screw (5) until the pressure gauge reading at pressure tap (2) is 24500 ± 1470 kPa (3550 ± 215 psi).

    Note: Turn adjustment screw (5) clockwise in order to increase the pressure. Turn adjustment screw (5) counterclockwise in order to decrease the pressure.

  1. Tighten locknut (3) to a torque of 29 ± 2 N·m (21 ± 1 lb ft).

    Note: Always make final pressure adjustment on pressure rise.

  1. Return the pressure setting of the blade main relief valve to the specification after adjusting the blade line relief valve.