725 and 730 Articulated Trucks Steering, Suspension, and Body Hoist Hydraulic Systems Caterpillar

Checking the Precharge

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Personal injury or death can result from improper accumulator charging. Dry Nitrogen is the only gas approved for use in the accumulator. Charging the accumulator with oxygen will cause an explosion. This danger will not happen if nitrogen cylinders with standard CGA (Compressed Gas Association, Inc.) Number 580 connections are used. When ordering nitrogen gas, be sure that the cylinders are equipped with CGA Number 580 connections. Do not use color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders Never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity).

Park the machine on a level surface. Move the parking brake control to the ENGAGED position and shut off the engine.

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Illustration 1	g00762415
Control valve (1) on the left side of the machine.

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Illustration 2	g00762425
Control valve (2) on the right side of the machine.

1. Lower the suspension by opening control valves (1) and (2) .

2. Close the control valves after the suspension has fully lowered.

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Illustration 3	g00763647

3. Remove guard (11) and remove protective cap (12) from the gas valve on the accumulator on the left side of the machine.

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Illustration 4	g00763646
175-5507 Nitrogen Charging Group

4. Ensure that valve (9) is closed.

5. Attach connector (8) to the gas valve on the accumulator.

6. Turn valve (7) clockwise until the valve contacts the stop. Gauge (10) will indicate the nitrogen gas pressure of the accumulator. The pressure should be 3100 kPa (450 psi).

7. If the pressure is high, the pressure must be decreased.

   1. Disconnect the coupler at valve (9) .

   2. Open valve (9) slightly in order to allow the pressure to decrease to 3100 kPa (450 psi).

   3. Close valve (9) when the pressure is correct.

8. If the pressure is low, the pressure must be increased.

   1. Close valve (9) and connect the hose to the coupler at valve (9).

   2. Attach regulator (4) to a nitrogen cylinder by using connection (6) .

   3. Open the valve on the nitrogen cylinder and rotate screw (3) until gauge (5) reads 3100 kPa (450 psi).

   4. Open valve (9) and allow the accumulator to charge.

9. Close valve (9) and close the valve on the nitrogen cylinder. Turn valve (7) counterclockwise until the valve contacts the stop.

10. Remove the nitrogen charging group from the machine.

11. Check the gas valve on the accumulator for leaks. Install protective cap (12) and install guard (11) .

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Illustration 5	g00764579
The accumulator is located beneath a panel on the right side of the machine.

12. Repeat steps 3 through 11 for the accumulator on the right side of the machine.

13. Set the suspension. Refer to Systems Operation, Testing and Adjusting, "Suspension Height (Front) - Check and Adjust".

Charging a Rebuilt Accumulator

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Personal injury or death can result from improper accumulator charging. Dry Nitrogen is the only gas approved for use in the accumulator. Charging the accumulator with oxygen will cause an explosion. This danger will not happen if nitrogen cylinders with standard CGA (Compressed Gas Association, Inc.) Number 580 connections are used. When ordering nitrogen gas, be sure that the cylinders are equipped with CGA Number 580 connections. Do not use color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders Never use an adapter to connect your nitrogen charging group to a valve outlet used on both nitrogen, oxygen, or other gas cylinders. BE SURE YOU USE DRY NITROGEN (99.8% purity).

1. Install the accumulators on the machine. Refer to Disassembly and assembly, RENR3447, "Suspension Accumulator - Remove and Install".

2. Raise the suspension fully. Refer to Systems Operation, Testing and Adjusting, "Suspension Height (Front) - Check and Adjust". This will fill the accumulators with oil.

3. Shut off the engine.

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Illustration 6	g00763646

4. Disconnect the coupler at valve (9) .

5. Ensure that valve (9) is closed.

6. Attach connector (8) to the gas valve on the accumulator on the left side of the machine. Turn valve (7) clockwise until the valve contacts the stop. Open valve (9) in order to vent any pressure from the gas side of the accumulator.

7. Turn valve (7) counterclockwise until the valve contacts the stop. Remove connector (8) from the gas valve on the accumulator. Close valve (9) .

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Illustration 7	g00764579
The accumulator is located beneath a panel on the right side of the machine.

8. Repeat steps 5 through 7 for the accumulator on the right side of the machine.

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Illustration 8	g00762415
Control valve (1) on the left side of the machine.

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Illustration 9	g00762425
Control valve (2) on the right side of the machine.

9. Lower the suspension by opening control valves (1) and (2).

   Note: Do not close the control valves.

10. Connect the coupler at valve (9) of the nitrogen charging group.

11. Ensure that valve (9) and screw (3) are closed.

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Illustration 10	g00763647

12. Remove guard (11) and remove protective cap (12) from the gas valve on the accumulator on the left side of the machine.

13. Attach connector (8) to the gas valve on the accumulator on the left side of the machine. Turn valve (7) clockwise until the valve contacts the stop.

14. Attach regulator (4) to a nitrogen cylinder by using connection (6) .

    Note: Ensure that the valve on the nitrogen cylinder is closed before you connect regulator (4) .

15. Open the valve on the nitrogen cylinder and rotate screw (3) until gauge (5) reads the correct pressure. The correct pressure is 3100 kPa (450 psi) at 21 °C (70 °F).

    Note: The pressure is for an ambient air temperature of 21 °C (70 °F). Adjust the pressure for other ambient conditions, as required. Refer to table 3.

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    Table 3

    Charging pressure and Temperature Relationship for a Typical 3102 kPa (450 psi) Accumulator
    Temperature	Pressure
    -7 °C (20 °F)	2807 kPa (407 psi)
    -1 °C (30 °F)	2866 kPa (416 psi)
    4 °C (40 °F)	2924 kPa (424 psi)
    10 °C (50 °F)	2983 kPa (433 psi)
    16 °C (60 °F)	3041 kPa (441 psi)
    21 °C (70 °F)	3100 kPa (450 psi)
    27 °C (80 °F)	3159 kPa (458 psi)
    32 °C (90 °F)	3217 kPa (466 psi)
    38 °C (100 °F)	3276 kPa (475 psi)
    43 °C (110 °F)	3334 kPa (483 psi)
    49 °C (120 °F)	3393 kPa (492 psi)

16. Open valve (9) and allow the accumulator to charge. Gauge (10) will show the same pressure as gauge (5) when the accumulator is fully charged.

17. Close valve (9) and rotate valve (7) counterclockwise until the valve contacts the stop. Close the valve on the nitrogen cylinder.

18. Remove the nitrogen charging group from the machine.

19. Check the gas valve on the accumulator for leaks. Install protective cap (12) and install guard (11) .

20. Repeat steps 12 through 19 for the accumulator on the right side of the machine.

21. Set the suspension. Refer to Systems Operation, Testing and Adjusting, "Suspension Height (Front) - Check and Adjust".