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Pressurized System! Hydraulic accumulators contain gas and oil under high pressure. DO NOT disconnect lines or disassemble any component of a pressurized accumulator. All gas pre-charge must be removed from the accumulator as instructed by the service manual before servicing the accumulator or any accumulator component. Failure to follow the instructions and warnings could result in personal injury or death. Only use dry nitrogen gas to recharge accumulators. See your Cat dealer for special equipment and detailed information for accumulator service and charging. |
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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. |
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Specification
Gas pressure is variable with temperature. Check the temperature of the air around the accumulator. In order to check the amount of charge in an accumulator, the accumulator must be at the same temperature as the surrounding air.
Note: The temperature of the accumulator may change as the accumulator is being charged due to the expansion or compression of the nitrogen charge. It may be necessary to charge the accumulator in several steps in order to ensure a correct charge.
| Charge Pressures and Temperatures | |
| Temperature | Pressure |
| −25°C (−13°F) | 1490 kPa (216 psi) |
| −20°C (−4°F) | 1520 kPa (220 psi) |
| −15°C (5°F) | 1550 kPa (225 psi) |
| −10°C (14°F) | 1580 kPa (229 psi) |
| −5°C (23°F) | 1610 kPa (233 psi) |
| 0°C (32°F) | 1640 kPa (238 psi) |
| 5°C (41°F) | 1670 kPa (242 psi) |
| 10°C (50°F) | 1700 kPa (247 psi) |
| 15°C (59°F) | 1730 kPa (251 psi) |
| 20°C (68°F) | 1760 kPa (255 psi) |
| 25°C (77°F) | 1790 kPa (260 psi) |
| 30°C (86°F) | 1820 kPa (264 psi) |
| 35°C (95°F) | 1850 kPa (268 psi) |
| 40°C (104°F) | 1880 kPa (273 psi) |
| 45°C (113°F) | 1910 kPa (277 psi) |
| 50°C (122°F) | 1940 kPa (281 psi) |
Introduction
The accumulator stores pilot pressure oil for use at the main control valves. During multiple operations, the pilot system will demand more oil in order to maintain valve operation. The accumulator provides pilot pressure oil to the pilot system, when the pilot pump flow is inadequate. Inadequate flow will cause sluggish implement control.
Required Tools
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| Illustration 1 | g01089423 |
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Tooling (A) |
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| Illustration 2 | g01784963 |
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This tooling group is used to test the pressure in the pilot manifold. |
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| Tool | Item | Qty | Part Number | Description |
|---|---|---|---|---|
| A | A1 | 1 | 8T-0856 | Pressure Gauge (0 to 6,000 kPa (0 to 870 psi)) |
| A2 | 1 | 6V-3989 | Fitting | |
| A3 | 2 | 6V-4143 | Quick Connect Coupler | |
| A4 | 1 | 177-7860 | Hose As | |
| F | F1 | 1 | 6V-3965 | Fitting |
| F2 | 1 | 3J-1907 | O-Ring Seal |
Test Procedure
Preliminary Test
- Start the engine. Place the hydraulic lockout lever in the UNLOCKED position.
- Position the implements 1 m (3.3 ft) from the ground.
- Shut off the engine by turning the start switch to the OFF position. When the engine has stopped, return the start switch to the ON position.
- Move the joysticks in order to lower the implements. When the accumulator circuit is functioning properly, there will be enough stored energy for approximately 20 seconds after a power loss in order to lower the implements to the ground safely.
- If the preliminary test fails and the implements are unable to be lowered to the ground safely after a power loss, proceed to test the accumulator circuit. Refer to “Testing the Accumulator (Nitrogen Gas Charge)”.
Testing the Accumulator (Nitrogen Gas Charge)
Note: Some accumulators do not have a charge pressure port. This type of accumulator cannot be recharged. The accumulator must be replaced. Replacement accumulators are equipped with a charge pressure port.
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| Illustration 3 | g02103574 |
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Cap for charging port on accumulator |
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- Refer to Special Instruction, REHS5464, “Accumulator Discharging and Charging Procedures” for the testing and charging procedure.
Note: If the pressure reading is within the specifications of Table 1, continue to test the operation of the check valve within the pilot manifold. Refer to “Testing the Check Valve (Pilot Manifold)”.
Testing the Check Valve (Pilot Manifold)
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| Illustration 4 | g02104695 |
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Typical example 1 Location of the check valve in the pilot manifold |
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| Illustration 5 | g02173723 |
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Typical example 2 Location of the check valve in the pilot manifold |
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If the check valve does not close properly during a loss of pilot pressure, the accumulator precharge pressure will exhaust before being able to provide lowering of the implements.
Note: Make sure that the accumulator has a proper nitrogen gas charge before attempting to test the check valve. An improperly charged accumulator may give indications of a problem with the check valve.
- Stop the engine. Release the pressure from the pilot hydraulic system. Refer to Testing and Adjusting, “Hydraulic System Pressure – Release”.
- Connect a 6000 kPa (800 psi) pressure gauge to port “PSA2” on the pilot manifold. Use tooling group (A) and tooling group (F) .
- Start the engine and place the hydraulic lockout lever in the UNLOCKED position.
- Shut off the engine by turning the start switch to the OFF position. When the engine has stopped, return the start switch to the ON position.
- After the power loss, the accumulator will still have pilot system pressure. Use the stopwatch to observe the pilot pressure. The pilot pressure should stay above 1035 kPa (150 psi) within 20 seconds. This pressure ensures that enough stored energy is available to lower the implements to the ground.
Note: When the pilot pressure in the accumulator is approximately 860 kPa (125 psi), the pressure will suddenly drop to zero. This sudden drop occurs because no oil is left in the accumulator.
- If the pilot pressure in the accumulator is below 1035 kPa (150 psi) or the pilot supply is exhausted in less than 20 seconds, the check valve within the pilot manifold is not working properly.
- Move the joysticks in order to release any pilot hydraulic pressure in the accumulator.
- Turn the start switch to the OFF position.
- Clean the check valve. The check valve is located behind the plug on the pilot manifold. Repeat steps 3 through 5. If the test fails, replace the check valve.
Charge Procedure
- Refer to Special Instruction, REHS5464, “Accumulator Discharging and Charging Procedures”.