631K and 637K Wheel Tractor-Scraper Systems Pump Control Valve (Cushion-Hitch) - Test and Adjust Caterpillar


Pump Control Valve (Cushion-Hitch) - Test and Adjust
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1.1. Specifications
2.1. Introduction
3.1. Required Tools
4.1. Test Preparation
5.1. Test Procedure
6.1. Adjustment Procedure

------ 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.


Specifications

Table 1
Cushion-Hitch Pressure 
Date  Equipment ID Code 
  Pressure Specification  Actual 
High Idle(1)  18700 ± 350 kPa (2712 ± 51 psi)   
(1) The cushion-hitch control switch must be in the OFF position.

Introduction

This test procedure checks the pressure setting of the cushion-hitch pump control valve

Required Tools



Illustration 1g01623868

Table 2
Tool  Item  Part Number  Description  Qty 
198-4240  Digital Pressure Indicator Gp   
  B1  198-4234  Digital Indicator 
  B2  251-9600  Pressure Sensor Gp (0 to 68,900 kPa (0 to 10,000 psi)) 
B3 198-4236  Adapter Cable As 

Test Preparation

Operate the engine to allow the temperature of the oil to increase in the cushion-hitch system. The cushion-hitch control switch must be in the OFF position. The load cylinder rods must be fully retracted.

  1. Move the machine to a smooth, horizontal location. Move the machine away from other operating machines and away from personnel. Place the transmission direction control switch in the NEUTRAL position. Engage the parking brake. Lower the bowl to the ground. Retract the ejector cylinder and disengage the cushion hitch. Shut off the engine and turn the engine start switch to the ON position. Place chocks in front of the wheels and behind the wheels.

  2. Move the control levers through the full range of travel. This movement of the levers will relieve any pressure that may be present in the hydraulic system. Turn the engine start switch to the OFF position.

  3. Slowly loosen the filler cap for the hydraulic oil tank to release the pressure.

Test Procedure

Note: The cushion-hitch control switch must be in the OFF position.



    Illustration 2g03721271
    View of the left-hand side of the hitch assembly
    (1) Test port

  1. Connect Tooling (B) to pressure tap (1).

  2. Start the engine and operate the engine at HIGH IDLE rpm.

  3. Observe the digital pressure indicator and continue to keep the cushion-hitch control switch in the OFF position. The reading on the gauge must attain 18700 ± 350 kPa (2712 ± 51 psi) which is the pressure setting of the pump control valve.

Adjustment Procedure



    Illustration 3g06218031
    Pump Control Valve

  1. Stop the engine. If the setting of the pump control valve on the cushion-hitch piston pump is incorrect, remove cover to the adjustment screw.

  2. Loosen the locknut (2) and turn the adjustment screw (3) clockwise to increase the pressure setting. Loosen the locknut and turn the adjustment screw counterclockwise to decrease the pressure setting.

  3. Tighten the locknut and install the cover.

    Note: Hold the adjustment screw while you tighten the locknut.

  4. Remove the system pressure then remove the test equipment and the adapter.

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