854K Wheel Dozer Electrohydraulic System Caterpillar

The pilot control actuator is an electrohydraulic valve that controls the pilot oil pressure to each end of the main control valve spools. When the solenoid for the pilot control actuator is activated, pilot oil pressure is drained to the hydraulic tank. The main control valve spool moves toward the activated pilot control actuator. When the implement control levers are in the HOLD position, there is full pilot oil pressure in the pilot control actuators at both ends of the main control valve spool.

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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, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products. Dispose of all fluids according to local regulations and mandates.

Table 1

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

(1)	Part of the 4C-4892 Hydraulic Test Fitting
(2)	The 198-4240 Digital Pressure Indicator is also available.

This procedure measures the oil pressure in the pilot control actuators. This procedure will allow you to verify if the pilot control actuators are functioning properly.

1. Connect the steering frame lock link.

2. Release the hydraulic system pressure. Refer to Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
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   Illustration 1	g02717950
   Location of the Pressure Taps (Pilot Control Actuator)

3. Attach test gauge (B) to test gauge hose (A). Attach test gauge hose (A) to the desired pressure tap.

4. Engage the parking brake.

5. Shift the transmission to neutral.

6. Start the engine and warm the hydraulic oil to 63° ± 25°C (145° ± 45°F).

7. With the engine at low idle, record the gauge reading.

With the control levers in the HOLD position, there must not be more than 275 kPa (40 psi) pressure difference in the pilot control actuator at each end of a valve spool. The pressure reading is expected to be pilot pressure.

The pilot chamber pressure should be equal to the hydraulic tank pressure when the pilot control valve is fully actuated.