AD30 Underground Articulated Truck Braking System Accumulator Charging Valve (Brake) - Test and Adjust Caterpillar

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Personal injury or death can result from escaping fluid under pressure. Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury. Always use a board or cardboard when checking for a leak.

Note: There are two separate procedures that may be used to check the operation of the accumulator charging valve and several associated components.

Reference: Procedure 1 is a quick method for checking the cut-out pressure. This procedure also indicates whether the brake accumulator oil pressure switch and the alert indicator are working correctly. The procedure provides an estimate of the accumulator precharge pressure and an estimate of the number of brake applications before the brake accumulator oil pressure alert indicator turns on.

Reference: Procedure 2 determines whether the cut-in pressure and the cut-out pressure are correct. This procedure also provides the steps for adjusting the brake accumulator charging valve.

Procedure 1

1. Stop the engine. Engage the parking brake. Depress the service brake pedal at least 70 times to remove the oil pressure from the brake accumulators.

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Illustration 1	g00984578
Location of the brake accumulator pressure taps (1) Brake accumulator oil pressure switch for the alert indicator (2) Accumulator charging valve (3) Rear brake accumulator pressure tap (4) Front brake accumulator pressure tap

2. Connect a hose assembly with an 8T-0859 Pressure Gauge (0 to 25,000 kPa (0 to 3,600 psi)) to pressure tap (3) or pressure tap (4) on accumulator charging valve (2) .

3. Observe the pressure gauge. Before the engine is started, the oil pressure must be 0 kPa (0 psi).

4. Start the engine. Allow the oil pressure to increase to the cut-out pressure. The correct cut-out pressure should be 14480 ± 345 kPa (2100 ± 50 psi).

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

6. Turn the engine start switch key to the ON position, but do not start the engine.

7. Apply the service brakes repeatedly, pausing for a second or two between each brake application. Count the number of brake applications. Observe the pressure gauge as you apply the brakes.

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Illustration 2	g00984579
AVSpare Monitoring System display (5) Brake accumulator oil pressure alert indicator

8. When the reading on the pressure gauge decreases to 8275 ± 345 kPa (1200 ± 50 psi) brake accumulator oil pressure alert indicator (5) on the dash panel should illuminate. This indicates the operational status of brake accumulator oil pressure alert indicator (5) . This also indicates the operational status of brake accumulator oil pressure switch (1) .

9. Continue to apply the service brakes. Pause for one or two second between each brake application. Also, continue counting the number of brake applications while observing the pressure gauge. When the pressure drops off rapidly, this indicates the approximate nitrogen precharge pressure in the brake accumulators.

10. Determine the number of brake applications that were required before the sudden pressure drop off in Step 9. The number of service brake applications should be approximately 65 times.

11. If the accumulator charging valve cut-out pressure is not within the specification, complete Steps 7 through 12 in "Procedure 2". If the nitrogen precharge pressure is not within the specification, test the brake accumulators for the correct charge pressure.

Reference: For the correct nitrogen precharge pressure and for information on testing the brake accumulators, refer to Brake Accumulator - Test and Charge, "Braking System, System Operation, Testing and Adjusting", for the machine that is being serviced.

Procedure 2

1. Stop the engine. Engage the parking brake. Depress the service brake pedal at least 70 times to remove the oil pressure from the brake accumulators.

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Illustration 3	g00984580
Location of the brake accumulator pressure taps (2) Accumulator charging valve (3) Rear brake accumulator pressure tap (4) Front brake accumulator pressure tap

2. Connect a hose assembly with an 8T-0859 Pressure Gauge (0 to 25,000 kPa (0 to 3,600 psi)) to pressure tap (3) or pressure tap (4) on accumulator charging valve (2) .

3. Observe the pressure gauge. Before the engine is started, the oil pressure must be 0 kPa (0 psi).

4. Start the engine. Raise the engine speed to the high idle rpm. Look for a stop (pause) in the increase in oil pressure. Make a record of the oil pressure at this point. This is the approximate nitrogen precharge pressure in the brake accumulators. If the precharge pressure is not within the specification, test the brake accumulators for the correct charge pressure.

   Reference: For the correct nitrogen precharge pressure and for information on testing the brake accumulators, refer to Brake Accumulator - Test and Charge, "Braking System, Systems Operation, Testing and Adjusting" for the machine that is being serviced.

5. The oil pressure must increase to a maximum pressure. Record this pressure. This is the cut-out pressure of the accumulator charging valve. The correct cut-out pressure should be 14480 ± 345 kPa (2100 ± 50 psi).

6. Apply the service brakes several times while the engine is running. Confirm that the pressure drops consistently. At the point of the specified cut-in, the pressure begins to increase quickly. The cut-in pressure should be 11720 ± 345 kPa (1700 ± 50 psi).

7. If the cut-in pressure and the cut-out pressure are not within the specification, stop the engine. Completely remove all the oil pressure from the brake circuit by repeating Steps 1 through 3

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Illustration 4	g00881990
Accumulator charging valve (6) Cover plug for the adjustment screw

8. Remove cover plug (6) for the adjustment screw.

Note: The charging limits will move together. The range between the cut-in pressure and the cut-out pressure is not adjustable.

9. Turn the hex plug that is located under cover plug (6) , by one quarter of a turn. Turning the hex plug clockwise will increase the cut-in pressure and the cut-out pressure. Turning the hex plug counter clockwise will decrease the cut-in pressure and the cut-out pressure.

10. Instal cover plug (6) on the accumulator charging valve.

11. Start the engine. Make sure that the cut-in pressure and the cut-out pressure are within the specification, repeat Steps 7 through 11.

12. If the cut-in pressure and the cut-out pressure can not be adjusted within the specification, the accumulator charging valve should be replaced or repaired.