938H Wheel Loader and IT38H Integrated Toolcarrier Hydraulic System Caterpillar

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Dry nitrogen is the only gas approved for use in the accumulators. The charging of oxygen gas in an accumulator will cause an explosion. An explosion can be eliminated by using nitrogen gas cylinders with standard CGA (Compressed Gas Association, Inc.) No. 580 connectors. When nitrogen gas is ordered, make sure to order the cylinders with CGA No. 580 connectors. Do not rely on color codes or other methods of identification to tell the difference between nitrogen and oxygen cylinders. In any application, 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).

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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.

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Personal injury can result from hydraulic oil pressure and hot oil. Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system. Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.

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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock.

Machine Preparation for Troubleshooting

1. Park the machine on a smooth, level surface. Park the machine away from working machines and personnel. Lower the work tool to the ground.

2. Allow only one operator on the machine. Keep all personnel away from the machine or in the view of the operator.

3. Move the transmission control lever to the NEUTRAL position.

4. Engage the parking brake.

5. Place the steering frame lock in the LOCKED position.

   ReferenceFor more information about preparing the machine for troubleshooting, refer to the Service Manual module Testing and Adjusting, "General Testing and Adjusting Information" for the machine that is being serviced.

Shutdown Procedure

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Illustration 1	g01410630
Location of ride control switch-on switch panel

1. Turn the ride control switch to the ON position. The switch for the ride control system is placed in the REARWARD position.

2. Lower the work tool to the ground.

3. Move the lift control lever to the FLOAT position.

4. Turn the engine start switch to the OFF position and remove the key.

Discharging the Accumulator

1. While the engine is running, turn the ride control switch to the ON position.

2. Lower the work tool to the ground. Then, move the lift control lever to the FLOAT position. This procedure will relieve all of the hydraulic pressure in the accumulator.

3. Turn the engine start switch to the OFF position. Disconnect the hydraulic lines for servicing, as needed.

   Note: If the accumulator must be replaced, perform Steps 1 through 3. Then, use the following procedure:

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   Illustration 2	g01522354
   Right side of the machine Location of the ride control accumulator

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   Illustration 3	g01522367
   Ride Control Accumulator (2) Nitrogen charging valve

   1. Remove the cap which protects nitrogen charging valve (2) .
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   Illustration 4	g00282185
   (3) Nipple. (4) Coupling assembly. (5) Pressure gauge. (6) Hose assembly. (7) Coupling assembly. (8) Nipple. (9) Valve. (10) Pressure gauge. (11) Regulator assembly. (12) Pressure regulating screw. (13) Chuck for the nitrogen cylinder valve. (14) Valve handle. (15) Nitrogen charging chuck. (16) Hose assembly. (17) Tee.

   2. Identify the correct nitrogen charging chuck.

      Note: For a nitrogen charging valve with a .305 inch -32 THD, use a 1S-8938 Nitrogen Charging Chuck and a 1U-5551 Extension Assembly . For a nitrogen charging valve with a .482 inch -26 THD, use a 7S-5106 Nitrogen Charging Chuck and a 7S-5439 Extension Assembly .

   3. Attach hose assembly (16) to nitrogen charging chuck (15) .

   4. Attach nitrogen charging chuck (15) and hose assembly (16) to nitrogen charging valve (2) .

   5. Place the open end of hose assembly (16) away from the work area and away from other personnel.
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   Illustration 5	g02442962

   6. Loosen the nut on the nitrogen charge valve all the way in the counterclockwise direction. Refer to illustration 5. This procedure will open the nitrogen charging valve (2) . This procedure will release all of the nitrogen from the accumulator through hose assembly (16) . Remove the hydraulic lines from the accumulator. Now, the accumulator can be removed from the machine.

Nitrogen Charging Procedure

1. Move the machine to a smooth, level surface.

2. Move the transmission control lever to the NEUTRAL position. Move the transmission neutral lock to the LOCKED position.

3. Engage the parking brake.

4. Start the engine. Keep the engine running during the following steps.

5. Move the lift control lever to the FLOAT position. Turn the ride control switch to the ON position. Refer to Illustration 1 for the location of the ride control switch.

6. Remove the cap which protects nitrogen charging valve (1) .

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Illustration 6	g00282185
(3) Nipple. (4) Coupling assembly. (5) Pressure gauge. (6) Hose assembly. (7) Coupling assembly. (8) Nipple. (9) Valve. (10) Pressure gauge. (11) Regulator assembly. (12) Pressure regulating screw. (13) Chuck for the nitrogen cylinder valve. (14) Valve handle. (15) Nitrogen charging chuck. (16) Hose assembly. (17) Tee.

7. Turn valve handle (14) on nitrogen charging chuck (15) all the way in the counterclockwise direction. Attach the appropriate nitrogen charging chuck (15) to nitrogen charging valve (2) .

   Note: For a nitrogen charging valve with a .305 inch -32 THD, use a 1S-8938 Nitrogen Charging Chuck and a 1U-5551 Extension Assembly . For a nitrogen charging valve with a .482 inch -26 THD, use a 7S-5106 Nitrogen Charging Chuck and a 7S-5439 Extension Assembly .

8. Attach hose assembly (16) between nitrogen charging chuck (15) and tee (17) . Install needle valve (9) on one of the connecting points of the tee. Install an 8T-0858 Pressure Gauge in the remaining open port on the tee. The pressure gauge is rated at 16000 kPa (2300 psi).

9. Install coupling assembly (7) in the open port of needle valve (9) .

10. Install nipple (8) on one end of hose assembly (6) . Place the open end of the hose assembly away from the work area and away from other personnel.

11. Open needle valve (9) and turn valve handle (14) on nitrogen charging chuck (15) all the way in the clockwise direction.

12. Raise the lift arms all the way in to purge the nitrogen charge momentarily.

13. Close needle valve (9) .

14. Lower the bucket to the ground. Move the lift control lever to the FLOAT position.

15. Attach the open end of hose assembly (6) to regulator assembly (11) . Install an 8T-0859 Pressure Gauge in the port that is directly above the regulator. This pressure gauge is rated at 25000 kPa (3600 psi).

    Install an 8T-0856 Pressure Gauge in the remaining port next to regulator assembly (11) . This pressure gauge is rated at 6000 kPa (870 psi).

16. Install regulator assembly (11) on nitrogen tank valve (2) . Adjust screw (12) on regulator (11) in order to set the pressure on the 8T-0856 Pressure Gauge to the appropriate charge pressure.

    Note: To ensure that the accumulator nitrogen charge is correct, the accumulator piston must be at the bottom of the accumulator cylinder. Nitrogen pressure varies with the temperature. To obtain the most accurate nitrogen charge, the temperature of the accumulator should equal the outside air temperature. However, the temperature of the accumulator could be higher than the outside air temperature in some cases. If so, the temperature of the accumulator should be used instead of the outside air temperature.

    Note: The pressures in the following table are recommended for machines with typical buckets (work tools) and with average payloads. The nitrogen pressure should be increased for machines with heavy buckets, work tools, or large payloads. This increase will keep the piston from contacting the stop during normal roading while the ride control system is on. Raising the nitrogen pressure will result in a stiffer ride.

    Note: Some contact between the piston and the internal stop is normal, when the machine rolls over large bumps.

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    Table 2

    Accumulator Precharge Pressure/Temperature Relationship for a Typical 3000 kPa (435 psi) Accumulator
    Temperature	Pressure (1)
    -7°C (20°F)	2707 kPa (393 psi)
    -1°C (30°F)	2766 kPa (401 psi)
    4°C (40°F)	2824 kPa (410 psi)
    10°C (50°F)	2883 kPa (418 psi)
    16°C (60°F)	2941 kPa (427 psi)
    21°C (70°F)	3000 kPa (435 psi)
    27°C (80°F)	3059 kPa (443 psi)
    32°C (90°F)	3117 kPa (452 psi)
    38°C (100°F)	3176 kPa (460 psi)
    43°C (110°F)	3234 kPa (469 psi)
    49°C (120°F)	3293 kPa (477 psi)

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    ( 1 )

    The nominal tolerance is ± 35 kPa (± 5 psi).

17. Open the needle valve (9) . The nitrogen pressure should appear on the 8T-0858 Pressure Gauge in 10 to 20 seconds.

    Note: If pressure appears on the gauge faster, close pressure regulating screw (12) on regulator assembly (11) and disconnect hose assembly (6) at coupling assembly (4) . Close needle valve (9) and remove coupling assembly (4) . Repeat Steps 5 through 17.

18. If the ride control accumulator is properly charged, then tighten the nut on the nitrogen charging valve in a clockwise direction. Turn tee handle (14) on nitrogen charging chuck (15) all the way in the counterclockwise direction. Close needle valve (9) .

19. Turn the valve on the nitrogen cylinder clockwise in order to shut off the flow of nitrogen. Turn screw (12) on regulator assembly (11) counterclockwise, until the pressure on gauge (5) goes back to zero.

20. Slowly disconnect hose (16) from needle valve (9) .

21. Open needle valve (9) before you remove nitrogen charging chuck (15) from nitrogen charging valve (2) on the accumulator.

22. Remove nitrogen charging chuck (15) from the ride control accumulator.

23. Install the protective cap on nitrogen charging valve (2) .

Road Test

Note: The pressures in Table 2 are recommended for machines with typical work tools. The nitrogen pressure should be increased for machines with heavy buckets, work tools, or large payloads. This increase will keep the piston from contacting the stop during normal roading while the ride control system is on. Raising the nitrogen pressure will result in a stiffer ride.

Note: Occasional contact between the piston and the internal stop is normal.

1. Put a typical load in the work tool.

2. Place the ride control switch to the OFF position.

3. Move the lift control lever to the LOWER position. Lift the front of the machine off the ground with the bucket. Place the lift control lever in the HOLD position.

4. Place the ride control switch into the ON position. The front of the machine should lower to the ground.

5. Place the ride control switch into the OFF position.

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Illustration 7	g01419433

6. Verify that the kick in speed for the ride control system is set at 10 km/h (6 mph). Verification of the kick in speed can be performed through Caterpillar Electronic Technician.

7. Place the ride control switch into the AUTO position. Ensure that the bucket is flat on the ground.

8. Move the lift control lever into the lower position in order to create a downward pressure on the bucket. Return the lift control lever to the HOLD position.

9. Move the machine in the forward direction to a speed of at least 10 km/h (6 mph). At a speed of 10 km/h (6 mph), the ride control system should activate. The downward pressure should disappear.