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Personal injury or death can result from sudden machine movement. Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine. To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section. |
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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 machine. 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 in Caterpillar machines. Dispose of all fluids according to local regulations and mandates. |
Note: Before you perform any tests, visually inspect the entire hydraulic system for oil leaks and for damaged components.
The 8T-5320 Hydraulic Test Group and the 4C-4890 Hydraulic Test Group may be used to test the pressure at the pressure tap.
The pulled unit dual stage relief valve is part of the pulled unit control valve. The pulled unit control valve is located under the machine. The relief pressure for the OPEN position is different from the relief pressure for the CLOSE position.
Relief Valve Test (High Pressure)
- Close the pulled unit. Stop the engine.
- Connect a hose assembly with an 8T-0860 Pressure Gauge (0 to 40000 kPa (0 to 5800 psi)) to the pressure tap for the front section of the pulled unit hydraulics and rear brake cooling gear pump.
- Start the engine. Operate the pulled unit repeatedly until the temperature of the hydraulic oil is above 38°C (100°F).
- Run the engine at high idle and move the hoist control to the OPEN position.
- After the pulled unit is fully opened, look at the gauge and hold the hoist control in the OPEN position. The high pressure gauge reading is the relief valve pressure setting. The correct pressure setting is 17225 to 17925 kPa (2500 to 2600 psi).
- As needed, adjust the number of shims in order to achieve the correct relief valve pressure setting.
Show/hide table
Table 1 Shims for Adjusting the Relief Valve Pressure Setting Part Number Thickness Pressure Change 5J-2721
0.13 mm (0.005 inch)
65 kPa (9 psi)5J-2722
1.22 mm (0.048 inch)
610 kPa (88 psi)
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| Illustration 1 | g00283734 |
High pressure relief valve (1) 5J-2721 Shim (2) 5J-2722 Shim | |
Relief Valve Test (Low Pressure)
- Close the pulled unit. Stop the engine.
- Connect a hose assembly with an 8T-0856 Pressure Gauge (0 to 6000 kPa (0 to 870 psi)) to the pressure tap for the front section of the pulled unit hydraulics and rear brake cooling gear pump.
- Start the engine. Operate the pulled unit repeatedly until the temperature of the hydraulic oil is above 38°C (100°F).
- Run the engine at high idle and move the hoist control to the CLOSE position.
- After the pulled unit is fully closed, look at the gauge and hold the hoist control in the CLOSE position. The high pressure gauge reading is the relief valve pressure setting. The correct pressure setting is 3450 to 3800 kPa (500 to 550 psi).
- As needed, adjust the number of shims in order to achieve the correct relief valve pressure setting.
Show/hide table
Table 2 Shims for Adjusting the Relief Valve Pressure Setting Part Number Thickness Pressure Change 5J-2721
0.13 mm (0.005 inch)
13 kPa (2 psi)5J-2722
1.22 mm (0.048 inch)
125 kPa (18 psi)
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| Illustration 2 | g00283735 |
Low pressure relief valve (3) 5J-2721 Shim (4) 5J-2722 Shim | |