349F and 352F Excavators Hydraulic System Caterpillar

Specification

Introduction

The main relief valve is located in the left side of the main control valve. The main relief valve limits the maximum operating pressure of the travel hydraulic circuit and the implement hydraulic circuits when the machine is at a load condition. Machines that are equipped with heavy lift have a high-pressure setting and a low pressure setting for the main relief valve.

Illustration 1	g02142184
Main relief valve location on main control valve

Required Tools

Illustration 2	g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

Machine Preparation

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

2. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "System Pressure - Release".
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   Illustration 3	g02142243
   Pressure tap for the drive pump

3. Attach a 41,368 kPa (6,000 psi) pressure sensor to the pressure tap for the drive pump.

Test Procedure

Standard

1. Start the engine.

2. 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.

3. Place the hydraulic activation control lever in the UNLOCKED position.

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

5. Move the joystick for the boom until the boom is at the full BOOM RAISE position (full extension of boom cylinders).

6. Check the pressure reading for the main relief valve pressure setting. Refer to Table 1.

7. Return the joystick for the boom to the NEUTRAL position.

Heavy Lift

Note: Machines that are equipped with heavy lift have a high-pressure setting and a low pressure setting for the main relief valve.

1. Start the engine.

2. 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.

3. Place the hydraulic activation control lever in the UNLOCKED position.

4. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).
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   Illustration 4	g02062913
   Switch for heavy lift

5. Set the switch for heavy lift to the OFF position. The indicator light should not be illuminated.

6. Move the joystick for the boom until the boom is at the full BOOM RAISE position (full extension of boom cylinders).

7. Check the pressure reading for the main relief valve pressure setting. Refer to Table 1.

8. Return the joystick for the boom to the NEUTRAL position.
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   Illustration 5	g02061934
   Switch for heavy lift

9. Set heavy lift switch (A) to the ON position. Make sure that the indicator light is on.

10. Move the joystick for the boom until the boom is at the full BOOM RAISE position (full extension of boom cylinders).

11. Check the pressure reading for the setting for heavy lift of the main relief valve. Refer to Table 1.

12. Return the joystick for the boom to the NEUTRAL position.

Adjustment Procedure

Standard

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Illustration 6	g02142898
Main relief valve (A) Adjustment screw (L) Locknut

1. Loosen the locknut and turn the adjustment screw until the pressure reading at the pressure tap for the drive pump is within the specification. Refer to Table 1.

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

   Note: Always make final pressure adjustments on pressure rise.

2. Tighten the locknut.

Heavy Lift

Illustration 7	g02142900
Main relief valve (heavy lift) (LH) Locknut for heavy lift (AH) Adjustment screw for heavy lift (LM) Locknut for main relief (AM) Adjustment screw for main relief

Illustration 8	g02142901
Cutaway of the main relief valve (heavy lift operation) (LH) Locknut for heavy lift (AH) Adjustment screw for heavy lift (LM) Locknut for main relief (AM) Adjustment screw for main relief

When the main relief pressure setting is adjusted, the pressure setting for heavy lift is not affected. When adjustment screw (AM) is turned counterclockwise in order to decrease the main relief setting, the pressure difference between the main relief setting and the pressure setting for heavy lift will increase. When adjustment screw (AM) is turned clockwise in order to increase the main relief setting, the pressure difference between the main relief setting and the pressure setting for heavy lift will decrease.

When the pressure setting for heavy lift is increased, the main relief setting is also increased. When the pressure setting for heavy lift is decreased the main relief setting is also decreased. The relief valve pressure setting for heavy lift and the relief pressure setting for the main relief are shown in Table 1.

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Illustration 9	g02061934
Switch for heavy lift

1. Heavy lift switch (A) must be set to the ON position. Make sure that the indicator light is on.

2. Loosen locknut (LM). Turn adjustment screw (AM) clockwise until the adjustment screw stops.

3. Tighten locknut (LM).

4. Loosen locknut (LH).

5. Move the joystick for the boom until the boom is at the full BOOM RAISE position (full extension of boom cylinders).

6. Check the pressure reading for the setting for heavy lift of the main relief valve at the pressure tap for the drive pump. Refer to Table 1.

7. Return the joystick for the boom to the NEUTRAL position.

8. Adjust the pressure setting for heavy lift to the specification. Turn the adjustment screw (AH) clockwise in order to increase the pressure. Turn the adjustment screw (AH) counterclockwise in order to decrease the pressure. Refer to Table 1.

   Note: Always make final pressure adjustments on pressure rise.

9. Tighten locknut (LH). Do not allow adjustment screw (AH) to move.
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   Illustration 10	g02062913
   Switch for heavy lift

10. Set heavy lift switch (A) to the OFF position. The indicator light should not be illuminated.

11. Loosen locknut (LM).

12. Adjust the main relief pressure setting to the specification by turning adjustment screw (AM) counterclockwise. Refer to Table 1.

    Note: Always make final pressure adjustments on pressure rise.

13. Tighten locknut (LM). Do not allow adjustment screw (AM) to move.

    Note: If the pilot line for heavy lift prevents proper adjustment of the relief valve settings, the line can be removed in order to make the adjustments. The machine will need to be off and the hydraulic system pressure will need to be released in order to remove the pilot line for heavy lift. Make adjustments to the relief valves and reconnect the pilot line before starting the machine and checking the pressure settings.