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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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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 |
| -40° C (-40° F) | 811 kPa (118 psi) |
-34.4° C (-30° F) |
833 kPa (121 psi) |
-28.9° C (-20° F) |
854 kPa (124 psi) |
-23.3° C (-10° F) |
876 kPa (127 psi) |
-17.8° C (0° F) |
898 kPa (130 psi) |
-12.2° C (10° F) |
920 kPa (133 psi) |
-6.7° C (20° F) |
941 kPa (137 psi) |
-1.1° C (30° F) |
963 kPa (140 psi) |
4.4° C (40° F) |
985 kPa (143 psi) |
10° C (50° F) |
1007 kPa (146 psi) |
15.6° C (60° F) |
1028 kPa (149 psi) |
21.1° C (70° F) |
1050 kPa (152 psi) |
26.7° C (80° F) |
1072 kPa (155 psi) |
32.2° C (90° F) |
1093 kPa (159 psi) |
37.8° C (100° F) |
1115 kPa (162 psi) |
43.3° C (110° F) |
1137 kPa (165 psi) |
48.9° C (120° F) |
1159 kPa (168 psi) |
54.4° C (130° F) |
1180 kPa (171 psi) |
60° C (140° F) |
1202 kPa (174 psi) |
| Accumulator Specification | |||
| Date | Equipment ID Code | ||
| Item | Specification | Actual | Engine Speed |
| Accumulator Charge Pressure | 1050 ± 100 kPa (152 ± 15 psi) |
High Idle | |
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) |
Test Preparation - Accumulator Leak Down
- Move the machine to a smooth horizontal location.
- Engage the parking brake.
- Lower all of the implements.
- Stop the engine.
- Turn the key to the ON position. Make sure that the implement lockout switch is turned to the UNLOCKED position. Move the implement control levers to all positions several times in order to release any pressure in the hydraulic system.
- Attach tooling (B) to pressure tap (CPG) .
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| Illustration 2 | g03664145 |
(CPG) Pressure tap for the charge pressure of the accumulator | |
Test Procedure - Accumulator Pilot Oil Pressure Leak Down
- Start the engine. Warm the hydraulic oil to a minimum temperature of 65° C (150° F).
- Record the pressure reading on pressure tap (CPG) .
- 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 (CPG) .
- 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 Preparation - Accumulator Charge Pressure
- Move the machine to a smooth horizontal location.
- Engage the parking brake.
- Lower all of the implements.
- Stop the engine.
- Turn the key to the ON position. Make sure that the implement lockout switch is turned to the UNLOCKED position. Move the implement control levers to all positions several times in order to release any pressure in the hydraulic system.
- Attach tooling (B) to pressure tap (CPG) on pilot manifold (2) . Use the pressure tap (CPG) for the accumulator charge pressure.
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| Illustration 3 | g03664145 |
(CPG) Pressure tap for the charge pressure of the accumulator | |
Test Procedure - Accumulator Charge Pressure
- 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 (CPG) should be 3275 ± 170 kPa (475 ± 25 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 5 and Step ,6 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 (1) is located on the pilot manifold.
Note: Do not attempt to charge the accumulator until all pressure has been removed from the pilot accumulator.
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| Illustration 4 | g03664149 |
- When all of the adjustments are complete, remove all tooling and reinstall all guards.