M318F, M320F and M322F Wheeled Excavators Hydraulic System Caterpillar

Specification

Introduction

Performing the following test procedures will help to determine if the cut out pressure is correct and if the low brake pressure indicator functions correctly. The following test procedures will also help determine if the precharge pressure for the accumulators is correct.

Required Tools

Illustration 1	g01623868
Tooling (B) 198-4240 Digital Pressure Indicator Gp

Machine Preparation

1. Clear all personnel from the machine and from the area around the machine.

2. Start the engine.
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   Illustration 2	g02449876
   Engine speed dial

3. Set the engine speed dial at "10".

4. Lower the left console.

5. Position the machine on level ground. Check the visibility and adjust the mirrors for the best vision close to the machine.

6. Fully depress the service brake pedal until the service brake pedal locks mechanically.

7. Increase the hydraulic oil temperature to 46° to 60° C (115° to 140° F).

8. Lower the stabilizers and the blade tip.

9. Fully extend the bucket cylinder and place the bucket on the ground.

10. Stop the engine.

11. Release the pressure in the hydraulic system.

    Note: Refer to Testing and Adjusting, "System Pressure - Release".

12. Raise the left console.
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    Illustration 3	g02418817
    Parking brake button located on the soft panel switch

13. Push down on the parking brake button in order to activate the parking brake.

    Note: The indicator light will be illuminated when the parking brake control is activated.

14. Depress the service brake pedal repeatedly until there is no brake oil pressure.
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    Illustration 4	g03739193
    View of the brake control valve which is located under the cab (1) Brake control valve (2) Accumulator charge pressure (3) Low brake oil pressure switch (4) Service brake accumulator charging pressure

15. Connect tooling (B2) 34,450 kPa (5,000 psi) pressure sensor to pressure taps (4) at port "S1" and port "S2".

16. Observe both pressure gauges. Before you start the engine, the oil pressure must be 0 kPa (0 psi).

Test Procedure

1. Start the engine.

2. Set the engine speed dial at "10".

3. Depress the service brake at least five times in order to warm up the hydraulic circuit and the hydraulic accumulators.

   Note: The temperature of the hydraulic accumulators must be equal to the temperature of the hydraulic oil. Equal temperature throughout the braking system will avoid having incorrect measurements that are caused by the immediate temperature change in the nitrogen gas. A fast pressure drop will occur as a result of having cold accumulators.

4. Allow the oil pressure to increase to the cut out pressure. Check the pressure at pressure taps (4) when the pressure stops increasing. Refer to Table 1 for the correct pressure.

5. If the cut-out pressure is correct, proceed to Step 6. If the cut-out pressure is not correct, proceed to the "Adjustment Procedure".

6. After the brake accumulators have been completely charged and the correct cut out pressure has been obtained, stop the engine.

7. Turn the engine start switch to the ON position, but do not start the engine.
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   Illustration 5	g02478318
   Low brake oil pressure indicator as displayed in the monitor.

8. Depress the service brake repeatedly. Pause for two seconds between applications. Count the number of applications while you observe the pressure gauge.

   Note: A minimum of one or two brake applications will decrease the brake accumulator oil pressure to 8,000 kPa (1,160 psi) and the monitor will display a "LOW BRAKE OIL ACCUMULATOR PRESSURE" warning.

   Note: A minimum of five brake applications is required before the brake accumulator oil pressure decreases to 4,500 kPa (653 psi). This decrease in pressure indicates the operational status of the indicator and of service brake oil pressure switch (4).

9. Continue to depress the service brake. Pause for two seconds between brake applications. When the pressure drops off rapidly, this pressure drop off indicates the approximate nitrogen pre-charge pressure in the brake accumulators. Refer to Table 1 for the correct pressure.

10. Determine the number of brake applications that were required before the sudden pressure drop in Step 9. This number should be more than five times.

11. If the nitrogen pre-charge pressure is not within the specification, refer to Special Instruction, REHS5464, "Accumulator Discharging and Charging Procedures" for the required tooling, and the testing and charging procedure.

    Note: Do not attempt to charge the accumulator until all pressure has been removed from the wheel brake accumulator.

Adjustment Procedure

If cut-out pressure at pressure taps (4) is too low, use the adjustment screw on accumulator charge pressure (2) to increase the cut-out pressure.

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Personal injury or death can result from sudden machine movement. Sudden movement of the machine can cause injury to persons on or near the machine. To prevent injury or death, make sure that the area around the machine is clear of personnel and obstructions before operating the machine.

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Illustration 6	g03739193
View of the brake control valve which is located under the cab (1) Brake control valve (2) Accumulator charge pressure (3) Low brake oil pressure switch (4) Service brake accumulator charging pressure

1. Loosen the locknut on accumulator charge pressure (2).

2. Turn the adjustment screw on accumulator charge pressure (2) clockwise until the pressure at pressure taps (4) are set to the correct pressure. Refer to Table 1 for the correct pressure.

   Note: Always make the final pressure adjustment on the pressure rise.

   Note: An adjustment to the cut out pressure will cause a change in the cut in pressure setting.

3. While the adjustment setscrew on accumulator charge pressure (2) is being held, tighten the locknut to the specified torque.

4. Repeat the "Test Procedure" until the wheel brake accumulator charge pressure has been met.