621H, 623H and 627H Wheel Tractor-Scrapers Hydraulic and Steering System Caterpillar


Relief Valve (Push-Pull) - Test and Adjust

Usage:

621H DBK

Specifications

Table 1
Bail Raise and Lower Pressure 
Date  Equipment ID Code 
  Pressure Specification  Actual 
Bail Raise at High idle  7600 ± 690 kPa (1100 ± 100 psi)   
Bail Lower at High Idle  3900 ± 690 kPa (565 ± 100 psi)   

Introduction

This test will verify that the push/pull relief valve is set to the correct pressure setting.

Refer to the Testing and Adjusting, "Machine Preparation for Troubleshooting" before starting the test.

Make the test and necessary adjustments to the BAIL RAISE pressure setting first. When the BAIL RAISE pressure setting of the pressure control valve has been corrected, the BAIL LOWER pressure setting will be set automatically.

------ WARNING! ------

Sudden movement of the machine or release of oil under pressure can cause serious injury to persons on or near the machine.

To prevent possible injury, perform the procedure that follows before testing and adjusting the hydraulic system.


Required Tools



Illustration 1g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

Table 2
Tool  Item  Qty  Part No  Description 
  198-4240  Digital Pressure Indicator Gp 
  A1  198-4234  Digital Indicator 
A2 198-4238  Pressure Sensor Gp
(0 to 34,450 kPa (0 to 5,000 psi)) 
A3 198-4236  Adapter Cable As 

Test Preparation

  1. Operate the machine until the hydraulic oil temperature reaches normal operating temperature.

  2. Park the machine on a hard, level surface. Move the transmission control lever to NEUTRAL position. Lower the Bowl. Stop the engine. Engage the parking brake.


    Illustration 2g03421385
    Rear of the Tractor, Left Side of the Transmission
    (1) Test port for the push/pull relief valve

  3. Remove dust cap from test port (1) for the push pull relief valve. Connect Tooling (A) to test port (1).

Test Procedure

Note: To check the BAIL RAISE pressure setting, the bail cylinder must be raised.

  1. Start the engine and operate at high idle.

  2. Place the bail switch in the BAIL RAISE position. Tooling (A) should read 7600 ± 690 kPa (1100 ± 100 psi).

Adjustment Procedure



Illustration 3g03421291
Push-Pull Control Valve
(3) Valve
(4) Piston
(5) Shims

If the pressure is not correct, stop the engine. Remove valve (3) from the push-pull control valve. Check piston (4) in order to make sure that the piston (4) is free and does not stick. The pressure can be changed by the addition of shims (5) or the removal of shims (5). Add shims (5) in order to increase the pressure. Remove shims (5) in order to decrease the pressure. One shim will change the pressure approximately 190 kPa (28 psi).

After the adjustment has been made, check the pressure in order to ensure that the setting is correct.

Test Procedure

Note: To check the BAIL LOWER pressure setting, the bail cylinder must be lowered.

  1. Start the engine. Lower the bail against the stops.

  2. With the engine at high idle and the solenoid switch in the BAIL LOWER position, tooling (A) should read 3900 ± 690 kPa (565 ± 100 psi).

  3. Remove test equipment.

Note: If the pressure setting for the BAIL RAISE has been adjusted, the BAIL LOWER pressure will automatically be correct. If the pressure is incorrect, check valve (3) in order to ensure that piston (4) moves freely.

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