793C and 793C XQ Off-Highway Truck Steering System Caterpillar

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Dry nitrogen is the only gas approved for use in the accumulator. Charging the accumulator with oxygen gas 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 you order nitrogen gas, be sure that the cylinders are equipped with CGA No. 580 Connections. Do not use color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders.

Do not use an adapter to connect the nitrogen charging equipment to a valve that can be used on oxygen cylinders or gas cylinders. Use dry nitrogen.

Check that the engine has not been running for at least five minutes. This will allow the oil level in the steering accumulators to decrease. The accumulator bladder must be on the bottom of the cylinder. This will ensure that the pressure of the nitrogen charge is correct.

The steering accumulator has a dry charge of 6550 ± 350 kPa (950 ± 50 psi).

Checking the Nitrogen Charge

Illustration 1	g00834546
Nitrogen charging group (Tool (A) ) (1) 162-4147 Hose As (2) 8S-4600 Fitting (3) 8S-1506 Coupling (4) 162-4146 Regulator (5) 1S-8938 Chuck (6) 7S-5106 Chuck (7) 8T-0859 Pressure Gauge (8) 8S-4599 Coupling (9) 2S-5244 Fitting (10) 1S-8937 Needle Valve (11) 2D-7325 Pipe Tee (12) 1S-8941 Hose As

1. Remove the cap from the top of the accumulator. Install Tool (B) on the accumulator valve.

2. Install chuck (5) onto Tool (B). If the chuck does not fit properly, use Tool (B) .

   Note: Do not connect the hose to valve (10). Make sure that valve (10) is closed.

3. Turn the valve on chuck (5) clockwise.

4. Use 16000 kPa (2321 psi) pressure gauge (7) to check the nitrogen charge in the accumulator.

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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.

5. The pressure on the gauge must be within the tolerances that are listed in Table 2.

6. If the pressure reading on the gauge is too high, lower the pressure by slowly opening valve (10) .

7. If the pressure reading on the gauge is too low, charge the accumulator.

Charging the Accumulator

1. Close valve (10) .

2. Connect the hose from valve (10) to regulator (4). The hose is part of Tool (A) .

3. Open the valve on the nitrogen cylinder. Adjust the screw on regulator (4) until the gauge on regulator (4) is at the pressure that will charge the accumulator. Use Table 2 as a reference for the correct charging pressure.

4. Open valve (10) and charge the accumulator.

5. When the pressure reading on gauge (7) and the reading on the gauge on regulator (4) are identical, shut valve (10). Allow a waiting period of ten minutes for the temperature of the nitrogen inside the accumulator to stabilize.

6. If there is a decrease in pressure on the gauge on regulator (4), open valve (10). This allows more nitrogen to enter the accumulator.

7. Repeat Steps 5 and 6 until the following items occur:
   • Pressure readings of the gauge on regulator (4) and on gauge (7) are identical.

   • Pressure readings do not change.

8. Close the valve on the nitrogen cylinder.

9. Turn the valve on chuck (5) counterclockwise.

10. Remove the test equipment.

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Illustration 2	g00834547
This is a typical view of the top of an accumulator. (C) 6E-3330 Seal (D) Cap

11. Inspect the 6E-3330 Seal (C) before the cap (D) is installed.

    Note: Replace the 6E-3330 Seal (C) if the seal is damaged.

Charging a Rebuilt Accumulator

Remove all nitrogen from the end of the accumulator.

After the accumulator is installed on the machine, use the following procedure to charge the accumulator:

1. Use the same equipment that was used to check the nitrogen charge in the accumulator.

2. Connect regulator (4) of Tool (A) to the nitrogen cylinder.

3. Turn the screw on regulator (4) counterclockwise in order to set the pressure to zero.

4. Turn the valve (10) clockwise in order to close the valve.

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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.

5. Attach the chuck (5) to the stem of the gas valve on the accumulator by turning the swivel on the chuck clockwise. Tighten the chuck (5) until the chuck is finger tight. Tighten the chuck (5) to an additional one quarter turn in order to seat the seal.

   Note: To prevent damage to the valve core for the accumulator, ensure that the tee handle on the chuck is turned completely counterclockwise before the chuck is installed on the valve stem for the accumulator. Do not force the chuck.

6. Connect the hose from the valve (10) to regulator (4). The hose is part of Tool (A) .

7. Turn the knob on the valve for the nitrogen cylinder clockwise in order to open the valve. The pressure gauge on the pressure regulator will show the pressure in the nitrogen cylinder. The pressure gauge on regulator (4) should show zero.

8. Turn the tee handle on the chuck clockwise until resistance is felt in order to unseat the valve core on the accumulator. Do not force the chuck.

9. Turn the screw on regulator (4) counterclockwise until the indicator needle on the pressure gauge on regulator (4) moves from zero.

10. Crack the valve (10) in order to slowly fill the bladder inside the accumulator. Allow the bladder to expand slowly in order to completely fill the inside of the accumulator cylinder.

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Illustration 3	g00834547
This is a typical view of the top of an accumulator. (C) 6E-3330 Seal (D) Cap

11. When the pressure reading on pressure gauge (7) and the pressure reading on the pressure gauge on regulator (4) are equal, shut the valve (10) .

12. Adjust the screw on regulator (4) until the pressure gauge on regulator (4) is at the pressure that will charge the accumulator. Use Table 2 as a reference for the correct charging pressure.

13. Open the valve (10) in order to charge the steering accumulator.

14. Adjust the valves until the pressure reading on gauge (7) and the pressure reading on the gauge on regulator (4) show the correct pressure. Allow a waiting period of ten minutes for the temperature of the nitrogen inside the accumulator to stabilize. If the nitrogen pressure charge is low, adjust the screw on the regulator (4) counterclockwise in order to increase the charge pressure.

15. If there is a decrease in pressure on pressure gauge (7), open the valve (10). This will allow more nitrogen to enter the steering accumulator.

16. Repeat Step 5 and Step 6 until the following conditions occur.
    • Gauge (7) and the gauge on regulator (4) show equal pressure.

    • Pressure readings do not change.

17. Close the valve on the nitrogen cylinder.

18. Turn the valve handle on chuck (5) counterclockwise or turn the valve handle on Tool (B) counterclockwise.

19. Remove the test equipment.

20. Replace the 6E-3330 Seal (C) before the cap (D) is installed.

    Note: The 6E-3330 Seal (C) is part of the bladder.