558 Forest Machine Machine Systems Relief Valve (Main) - Test and Adjust Caterpillar


Relief Valve (Main) - Test and Adjust
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1.1. Specification
2.1. Introduction
3.1. Required Tools
4.1. Machine Preparation
5.1. Test Procedure
6.2. Standard
7.2. Heavy Lift
8.1. Adjustment Procedure
9.2. Standard
10.2. Heavy Lift

Specification

Table 1
"Relief Valve (Main) - Test and Adjust" 
Machine Settings  Engine Speed 
Speed Dial "10"
AEC switch OFF
Item  Specification  Actual 
Standard  35000 ± 500 kPa (5076 ± 73 psi)   
Heavy Lift  38000 ± 500 kPa (5512 ± 73 psi)   

Introduction

The main relief valve is located in the front side of the main control valve toward the bottom. The main relief valve is accessible from below the machine after removal of the access plate. 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 1g03688931
Main relief valve location on main control valve

Required Tools



Illustration 2g01623868
Tooling group "B"
198-4240 Digital Pressure Indicator Gp

Table 2
Tool  Item  Part Number  Description  Qty 
198-4240  Digital Pressure Indicator Gp   
  B1  198-4234  Indicator 
B2 198-4239  Pressure Sensor 41,368 kPa (6,000 psi) 
B3 198-4236  Extension Cable 

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".


    Illustration 3g03862183
    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 hydraulic activation control lever in the UNLOCKED position.

  3. 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.

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

  5. Move the joystick for the bucket until the bucket is at the full BOOM RAISE position (full extension of the 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 hydraulic activation lever to the UNLOCK position.

  3. 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.

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


    Illustration 4g02062913
    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 bucket until the bucket is at the full BUCKET CLOSE position (full extension of bucket cylinder).

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

  8. Return the joystick for the bucket to the NEUTRAL position.


    Illustration 5g02061934
    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

  1. Remove the access plate below the main control valve to locate the main relief valve.


    Illustration 6g02102305
    Main relief valve
    (A) Adjustment screw
    (L) Locknut

  2. Loosen locknut (L).

  3. Move the joystick for the bucket until the bucket is at the full BUCKET CLOSE position (full extension of the bucket cylinder).

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

  5. Return the joystick for the bucket to the NEUTRAL position.

  6. Adjust the pressure setting for the main relief valve to the specification.

    Note: Turn adjustment screw (A) clockwise to increase the pressure. Turn adjustment screw (A) counterclockwise to decrease the pressure.

    Note: Always make final pressure adjustments on pressure rise.

  7. Tighten locknut (L). Do not allow adjustment screw (A) to move.

Heavy Lift



Illustration 7g02061719
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 8g03737052
Cutaway of the 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

When the main relief pressure setting is adjusted, the pressure setting for heavy lift is not affected. When adjustment screw (AM) is turned counterclockwise 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 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.

  1. Remove the access plate below the main control valve to locate the main relief valve.


    Illustration 9g02061934
    Switch for heavy lift

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

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

  4. Tighten locknut (LM).

  5. Loosen locknut (LH).

  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 setting for heavy lift of the main relief valve. Refer to Table 1.

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

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

    Note: Always make final pressure adjustments on pressure rise.

  10. Tighten locknut (LH). Do not allow adjustment screw (AH) to move.


    Illustration 10g02062913
    Switch for heavy lift

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

  12. Loosen locknut (LM).

  13. Move the joystick for the bucket until the bucket is at the full BUCKET CLOSE position (full extension of the bucket cylinder).

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

  15. Return the joystick for the bucket to the NEUTRAL position.

  16. 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.

  17. 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 to make the adjustments. The machine will need to be off and the hydraulic system pressure will need to be released 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.

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