611 Wheel Tractor-Scraper Hydraulic System Caterpillar

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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 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 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).

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Sudden movement of the machine or release of oil under pressure can cause serious injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the hydraulic system.

Refer to Systems Operation, Testing and Adjusting, "Machine Preparation for Troubleshooting" before you begin the test.

Illustration 1	g01037517
(1) Pressure regulating screw (2) Pressure gauge (3) Regulator (4) Valve handle (5) Connection to the nitrogen cylinder (6) Chuck (7) Valve handle (8) Pressure gauge

Illustration 2	g01037516
(9) Cover (10) Seal

Use Tooling (A) in order to test the accumulator. The nitrogen charging group should also be used in order to charge the accumulator with the dry nitrogen gas.

Make sure that only dry nitrogen gas is used to charge the accumulator.

Turn off the engine. Make sure that the engine has not been operating for at least 5 minutes. This time period is long enough to allow the hydraulic oil to flow out of the bottom chamber of the accumulator. The piston in the accumulator must be on the bottom of the cylinder of the accumulator. This piston must be on the bottom of this cylinder in order to charge the accumulator correctly.

The charging pressure of the accumulator is approximately 3100 kPa (450 psi) at a temperature of 21°C (70°F).

The air temperature outside the accumulator is the ambient temperature. Before the dry nitrogen pressure in the accumulator may be accurately checked, the temperature of the accumulator must be equal to the ambient temperature. Before the accumulator may be correctly charged, the temperature of the accumulator must be equal to the ambient temperature.

Use Table 2 in order to determine the correct charging pressure at a given ambient temperature.

Checking the Dry Nitrogen Pressure in the Accumulator for the Axle Suspension

The dry nitrogen gas is contained in the end of the accumulator.

1. Remove cover (10) and seal (9) from the valve assembly on the top of the accumulator.

2. Install Tool (B) into the quick disconnect on Tool (C). Tool (B) is a 25000 kPa (3500 psi) pressure gauge. This pressure gauge should be used in order to check the nitrogen pressure in the accumulator. Close Tool (C) .

3. Install Tool (D) on the valve on the top of the accumulator.

4. Turn valve handle (4) on Tool (D) fully to the right. Measure the temperature of the air that is outside of the accumulator. This outside temperature is the ambient temperature. Locate this ambient temperature in the left column of Table 2. Read this row in order to determine the correct charging pressure. The reading on Tool (B) corresponds to the pressure of the dry nitrogen gas in the accumulator. The nitrogen pressures for the accumulator must be within the tolerances. Check tolerances in Table 2.

5. Decrease the nitrogen pressure if the nitrogen pressure is greater than the specified value in Table 2. Decrease the nitrogen pressure by slowly opening Tool (C) .

6. Increase the nitrogen pressure if the nitrogen pressure is less than the specified value in Table 2. Increase the nitrogen pressure to the specified level. Increase the nitrogen pressure according to "Charging the Accumulator for the Axle Suspension".

Charging the Accumulator for the Axle Suspension

Increase the nitrogen pressure in the accumulator according to the following steps:

1. Connect Tool (E) to Tool (F) on the nitrogen cylinder and Tool (C) .

2. Close Tool (C). Open the valve on the nitrogen cylinder. Adjust pressure regulating screw (1) on Tool (F). Adjust pressure regulating screw (1) until pressure gauge (2) is at the correct charging pressure. Use Table 2 to determine the correct charge pressure.

3. Open Tool (C). Charge the accumulator. Close Tool (C). Compare the reading on pressure gauge (2) with the reading on Tool (B). If these two readings are equal and these two readings remain constant, the accumulator has been correctly charged.

   If there is a decrease in the reading on Tool (B), open Tool (C). Allow more of the dry nitrogen gas to flow into the accumulator. Repeat this procedure until pressure gauge (2) and Tool (B) have the same reading. These two readings do not change when Tool (C) is closed.

4. Close Tool (C). Close the valve on the nitrogen cylinder.

5. Turn valve handle (4) on Tool (D) fully to the left.

6. Remove the charging equipment.

Charging a Rebuilt Accumulator for the Axle Suspension

When the accumulator has been rebuilt, the air must be removed from the upper chamber of the accumulator. When the accumulator has been rebuilt, insert approximately 1.9 L (2.0 qt) of SAE 10W hydraulic oil into the upper end of the accumulator. The hydraulic oil will be used to remove air from the upper chamber of the accumulator. This hydraulic oil also lubricates the top seal of the piston in the accumulator.

Install the rebuilt accumulator on the machine. Follow the steps below in order to remove the air from the upper chamber of a rebuilt accumulator. The following steps will enable you to charge a rebuilt accumulator.

1. Install Tooling (A) .

2. Turn valve handle (4) on Tool (D) fully to the right. Open Tool (C) .

3. Start the engine. Allow the engine to warm up. Move the cushion-hitch switch to the CUSHION RIDE position.

   Hydraulic oil will flow into the bottom of the accumulator. The air will first be forced out of the upper chamber of the accumulator through the test equipment. Then, the hydraulic oil will be forced out of the upper chamber of the accumulator through the test equipment. When the hydraulic oil stops flowing out of the top of the accumulator, the upper chamber of the accumulator will contain no air.

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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.

4. CloseTool (C) .

5. Turn off the engine. Wait for 5 minutes in order to allow the hydraulic oil pressure to decrease. The piston in the accumulator will be at the top of the accumulator.

6. Charge the accumulator according to the procedure in "Charging the Accumulator for the Axle Suspension". Rebuilt accumulators require longer charging times. New accumulators require less charging time. When the accumulator has been rebuilt, the piston is located in the top of the cylinder. The piston will be forced to the bottom of the cylinder during the charging procedure.