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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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| 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, "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. |
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For all relief valve tests, the recommended method to test a relief valve is to remove the valve from the machine and use a test bench to test and adjust the valve. This will help reduce hydraulic oil contamination in the hydraulic system. |
| Required Tools | ||
| Part Number | Description | Qty |
| 1U-5481 | Pressure Gauge Group | 1 |
| 1U-5482 | Pressure Adapter Group | 1 |
| 8S-7630 (1) | Stand | 2 |
| 8S-7641 (1) | Tube | 2 |
| 8S-8048 (1) | Saddle | 2 |
| 8S-7615 (1) | Pin | 2 |
| ( 1 ) | Optional tooling |
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| Illustration 1 | g00282695 |
Relief Valve (Typical Example) (1) Adjusting screw. (2) Locknut. (3) Valve body. | |
- Start the engine. Run the engine at high idle. Operate the implement control levers and move all of the cylinders in order to increase the temperature of the hydraulic oil to normal operating temperatures.
- Release the pressure in the hydraulic system. For more information about releasing hydraulic system pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.
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| Illustration 2 | g00298585 |
Jack Stands | |
Note: To improve access to the relief valves, rest the lift arms or the work tool on jack stands.
- Remove the cover that is over the control valve in order to access main relief valve (4) .
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| Illustration 3 | g00282870 |
Loader Tower Access Panel Lift arms raised for photographic purposes only. | |
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| Illustration 4 | g00757562 |
Main Control Valve (Typical Example) (4) Main relief valve. | |
- Attach a hose assembly onto pressure tap (6). Attach the hose assembly to the 8T-0852 Pressure Gauge (0 to 40,000 kPa (0 to 5,800 psi)).
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| Illustration 5 | g00757566 |
(5) Implement pump. (6) Pressure tap. | |
- Start the engine.
- Raise the bucket or the work tool off the ground or the jack stands (if used). Tilt back the bucket or the work tool until the cylinder rods are fully retracted.
- Increase the engine speed to high idle. Observe the pressure gauge and move the tilt control lever to the TILT BACK position. The pressure setting of main relief valve (4) should be 24800 ± 300 kPa (3600 ± 45 psi).
Note: In the following step, do not keep the tilt control lever in the TILT BACK position for more than five seconds while the pressure is at the relief valve setting.
- If the pressure is correct, lower the bucket or the work tool to the ground. Stop the engine and remove the test equipment.
If the cracking pressure of main relief valve (4) is not at the specification, use the following procedure to adjust main relief valve (4) :
- Stop the engine.
- Loosen locknut (2). Turn adjusting screw (1) clockwise in order to increase the relief valve setting. Turn adjusting screw (1) counterclockwise in order to decrease the relief valve setting.
- After adjusting screw (1) is turned for an adjustment, tighten locknut (2) to a torque of 50 ± 7 N·m (37 ± 5 lb ft).
- Perform Steps 5 through 8 in order to check the main relief valve pressure.