834G Wheel Dozer and 836G Landfill Compactor Electrohydraulic System Caterpillar

The pressure reducing valve is used to regulate the pressure of the hydraulic oil that is used for the auxiliary supply of pilot oil. The auxiliary supply of pilot oil is used to lower the work tools to the ground when the engine is not running. The oil is supplied from the lift hydraulic circuit. The oil flows from the lift cylinder through the check valves to the pressure reducing valve to a resolver to the actuators on the main implement valve.

Table 1

Required Tools
Tool	Part Number	Part Description	Qty
A	Test Gauge Hose
	6V-4143	Coupler (2)	1
	177-7860	Hose Assembly (1)	1
	8T-4188	Union Adapter (1)	1
	6V-3966	Fitting (1)	1
B	Test Gauge
	8T-0855	Pressure Gauge (1)	1
	6V-4144	Coupler (1)	1

( 2 )

Part of 4C-4892 ORFS Fittings Group

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the work tools have been lowered to the ground, and the oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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NOTICE
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates.

Machine Preparation

Prepare the machine for testing by completing the procedure that is specified in the Service Manual module Testing and Adjusting, "Machine Preparation for Troubleshooting" for the machine that is being serviced.

Testing and Adjusting Procedure

Illustration 1	g00726244
Left Side view of the Machine (1) Test Port for the Pilot Supply Pressure

1. Connect test gauge hose (A) and test gauge (B) to pressure tap (1) .

2. Engage the parking brake.

3. Shift the transmission to neutral.

4. Start the engine. Warm the hydraulic oil to normal operating temperature of approximately 49 °C (120 °F).

5. Raise the blade approximately 0.9 m (3 ft) off the ground.

6. Turn the engine off.

7. Turn the engine start switch to the ON position.

8. Observe the pressure reading while the blade is not moving. The oil pressure should be 1650 ± 150 kPa (240 ± 20 psi). If the pressure reading is not within the specification, perform the following adjustment.

   Proceed to Step 13 if the pressure setting is correct.

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Illustration 2	g00726246
View of the Pressure Reducing Valve Locknut (2). Adjusting screw (3) .

9. Loosen locknut (2) .

10. Turn adjusting screw (3) clockwise in order to increase the pressure setting. Turn adjusting screw (3) counterclockwise in order to decrease the pressure setting.

11. Tighten locknut (2) .

12. Repeat Steps 1 through 12 in order to obtain the proper pressure setting.

13. Remove test gauge hose (A) and test gauge (B) from the machine.