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Hot hydraulic oil under high pressure can remain in the components of the hydraulic system or the power train system after the engine has been stopped. The uncontrolled release of the hydraulic oil can cause sudden machine movement and can also result in the following conditions:
If hydraulic oil penetrates body tissue, the injury must be treated immediately by a doctor who is familiar with this type of injury. Use a board or a piece of cardboard to check for a hydraulic oil leak. Make sure that all of the attachments have been lowered to the ground and that all trapped pressure has been released from the hydraulic system and the power train system. Also, make sure that the hydraulic oil is cool before the removal of any components or lines. Remove the hydraulic 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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| NOTICE |
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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, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products. Dispose of all fluids according to local regulations and mandates. |
Specifications
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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. |
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Nitrogen gas pressure varies with the temperature. To obtain the most accurate nitrogen charge, the temperature of the accumulator must be identical to the air temperature around the accumulator.
Note: Adjust the pressure for ambient conditions, as required. Refer to the following table for the accumulator precharge pressure/temperature relationship.
| Charging Pressure for the Accumulator at Different Temperatures | |
| Temperature | Pressure |
| -1 °C (30 °F) | 1472 kPa (213 psi) |
10 °C (50 °F) |
1536 kPa (223 psi) |
21 °C (70 °F) |
1600 kPa (232 psi) |
32 °C (90 °F) |
1663 kPa (241 psi) |
43 °C (110 °F) |
1727 kPa (251 psi) |
| D7E Test for the accumulator pressure | ||
|---|---|---|
| Date | Equipment ID Code | |
| Item | Specification | Actual |
| Engine speed | High Idle | |
| Charge pump discharge pressure. | 3100 ± 100 kPa (450 ± 15 psi) |
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Introduction
The accumulator stores hydraulic oil pressure that can be used to lower the implements when the engine is off. The accumulator is located on the pilot manifold.
The following procedure will determine if the accumulator for the pilot system is charged to the appropriate pressure.
Required Tools
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| Illustration 1 | g02726620 |
Tooling (B) | |
| Tool | Item | Qty | Part Number | Description |
|---|---|---|---|---|
| B | B1 | 1 | 8T-0856 | Pressure Gauge (0 to 6,000 kPa (0 to 870 psi)) |
| B2 | 1 | 6V-3989 | Fitting | |
| B3 | 2 | 6V-4143 | Quick Connect Coupler | |
| B4 | 1 | 177-7860 | Hose As (10 ft) |
Machine Preparation
- Move the machine to a smooth horizontal location.
- Place the steering control lever in the NEUTRAL position.
- Engage the parking brake.
- Lower the attachments to the ground.
- Stop the engine.
- Turn the key to the ON position, but do not start the engine.
- Verify that the implement lockout switch is in the UNLOCKED position.
- Move the control levers through the full range of travel several times. This will relieve any pressure that may be present in the implement hydraulic system.
- Make sure that the pressure in the entire hydraulic system has been released.
- Turn the key to the OFF position.
- Observe the state of the amber hazardous voltage present lamp. If the lamp is illuminated, do not perform any type of service on the machine. Wait until the lamp is not illuminated. Then, perform the lamp test in the next step.
- While you observe the lamp, turn the disconnect switch to the OFF position. Then turn the disconnect switch to the ON position.
Note: When the disconnect switch is cycled, the amber hazardous voltage present lamp will illuminate briefly. Then, the lamp will turn off. This indicates that the operation of the lamp is correct.
- If an error message for the lamp circuit is displayed, or if the operation of the hazardous voltage present lamp does not appear to be correct, refer to the Troubleshooting, "General Information" section of the manual for information on troubleshooting the lamp circuit.
- Once the hazardous voltage level has been verified to be below 50.0 VDC, the machine can be serviced. Proceed to the next step.
- Locate the pressure test port on the accumulator manifold. The accumulator manifold is located on the front of the hydraulic tank on the left side of the tractor.
- Open access doors (1) and (2) .
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| Illustration 2 | g01946780 |
- Attach tooling (B) to pressure port (AP) on the accumulator manifold.
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| Illustration 3 | g01947147 |
(3) Accumulator for steering and braking system (4) Accumulator for the implement system (HPS) Pressure port for pilot supply pressure after the pilot shutoff valve (AP) Pressure port for pilot supply pressure (S) Pressure port for steering charge and pilot pump | |
Note: This test will only test the accumulator for the implement system (4) . In order to test the accumulator for steering and braking system (3) , the accumulators must be switched.
Test Procedure - Accumulator Pilot Oil Pressure Leak Down
- Complete steps in "Machine Preparation" then continue with step 2.
- Start the engine. Warm the hydraulic oil to a minimum temperature of 65° C (150° F).
- Record the pressure reading on pressure tap (AP) .
- Stop the engine. Turn the key to the ON position but do not start the machine.
- With the implement lockout switch in the UNLOCKED position, record the pressure reading at pressure tap (AP) .
- The pressure reading should not drop more than 700 kPa (101 psi) in 2 minutes. If a pressure drop greater than 700 kPa (101 psi) occurs, the pilot oil system should be checked for excessive leakage.
Adjustment Procedure - Pressure Leak Down
There are no adjustments that can be made to reduce pressure leaks in the system. Investigate the components of the charging system to determine the cause of the system leakage.
Test Procedure (Accumulator Charge Pressure)
- Complete steps in "Machine Preparation" then continue with step 2.
- Start the engine. Warm the hydraulic oil to a minimum temperature of 65° C (150° F).
- Operate the engine at HIGH IDLE.
- Exercise the implement hydraulics. At the accumulator, the pilot pressure at tooling (AP) should be 3100 ± 100 kPa (450 ± 15 psi).
- Shut off the engine. Turn the key to the ON position. The accumulator charge pressure should remain steady until an implement control is exercised.
- With the implement lockout switch in the UNLOCKED position, move the implement control out of the HOLD position in any direction in order to actuate a function. Return the handle to the hold position between activations of the handle. Quick movement of the handle should increase the accuracy of this test.
- With the handle in the HOLD position between activations, record the reading on tooling (B) .
- Repeat Step 6 and Step ,7 recording the reading each time the handle is returned to the HOLD position until the pressure reading at tooling (B) is zero.
- The last pressure reading recorded on tooling (B) is a close approximation of the nitrogen precharge in the accumulator.
- Refer to Table 1 for the appropriate accumulator charge.
- If the precharge of the original accumulator is out of the specifications, the accumulator will need to be replaced. The replacement accumulator has a charging valve and may be charged if needed.
Charging Procedure - Accumulator Charge
- Refer to Special Instruction, REHS5464, "Accumulator Discharging and Charging Procedures".
- The accumulator is located on the pilot manifold. Charging valve (6) is located on the top of the accumulator under the cap (5) .
Note: Do not attempt to charge the accumulator until all pressure has been removed from the pilot accumulator.
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| Illustration 4 | g01947173 |
(5) Cap (6) Charging valve (7) Accumulator | |
- When all of the adjustments are complete, remove all tooling and reinstall all guards.