769D Off-Highway Truck Hydraulic System: Hoist Cylinder Performance - Test & Relief Valve (Hoist Dual Stage) - Test and Adjust

1.-Hoist Cylinder Performance - Test

WARNING: 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.

1. Start the engine. Operate the engine at high idle.

2. Move the hoist control to the RAISE position. Hold the hoist control in the RAISE position for five seconds after the dump body is fully raised. Then, lower the dump body all the way to the truck frame.

3. Repeat Step 2 until the temperature of the hydraulic oil is between 65 °C (150 °F) and 121 °C (250 °F).

Cycle Times for Hoist Cylinders

1. Lower the dump body to the truck frame.

2. Operate the engine at high idle.

3. Raise the dump body to the fully raised position. Use a stopwatch to measure the required time.

The required time for full extension of the hoist cylinders is 9 ± 1 seconds.

The required time for full lowering of the hoist cylinders is 7 ± 1 seconds.

With the body down snub function and the body float function in the OFF position, the required time for full lowering of the hoist cylinders is 7 ± 1 seconds.

Cylinder Drift

Note: Perform this test with an empty dump body and hydraulic oil above 38°C (100°F).

1. Move the hoist control to the RAISE position.

2. When the first stage of the hoist cylinders is extended by 305 mm (12 inch), move the hoist control to the HOLD position.

3. The dump body will push the cylinder head of the first stage by 6.35 mm (0.250 inch) onto the second stage of the hoist cylinders. Use a stopwatch and record the required time.

The acceptable time for cylinder drift is relative to the temperature of the hydraulic oil in the hoist cylinders. See Table 1 for the acceptable time.

Table 1

Acceptable Cylinder Drift
Minutes	Oil Temperature	Cylinder Drift
2.7	38° to 48°C (100° to 119°F)	6.35 mm (0.250 inch)
1.2	49° to 64°C (120° to 149°F)	6.35 mm (0.250 inch)
1.0	65 °C (150 °F)	6.35 mm (0.250 inch)

Excessive cylinder drift can be caused by the following conditions:

• Leaks in the lines between the hydraulic oil tank and the hoist cylinders
• Worn control valve spool
• Worn seals in the hoist cylinders

2.-Relief Valve (Hoist Dual Stage) - Test and Adjust

Table 1

Tools Needed	Qty
6V-3079 Pressure Hose Assembly	1
6V-4143 Coupler Assembly	2
8T-0856 Pressure Gauge ( 6000 kPa (870 psi))	1
8T-0860 Pressure Gauge ( 40000 kPa (5800 psi))	1

Note: Make sure that the filters and the screens are clean before you test any pressures. Make sure that the oil is at operating temperature before you perform this test.

Note: Before you perform any tests, visually inspect the entire hydraulic system for oil leaks and for damaged components.

WARNING: 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.

NOTICE
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 Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Caterpillar products.Dispose of all fluids according to local regulations and mandates.

(1) High pressure relief valve (2) Low pressure relief valve (3) Hoist dual stage relief valve(4) Hoist control valve

Hoist dual stage relief valve (3) is part of the hoist control valve (4). The relief pressure for the RAISE position is controlled by high pressure relief valve (1). The relief pressure for the LOWER position is controlled by low pressure relief valve (2) .

Relief Valve Test (High Pressure)

(5) Pressure tap

1. Lower the dump body. Stop the engine.

2. Connect a hose assembly with an 8T-0860 Pressure Gauge (0 to 40000 kPa (0 to 5800 psi)) to pressure taps (5) .

3. Start the engine. Operate the dump body repeatedly until the temperature of the hydraulic oil is above 38°C (100°F).

4. Run the engine at high idle and move the hoist control to the RAISE position.

5. After the dump body is fully raised, look at the gauge and hold the hoist control in the RAISE position. The high pressure gauge reading is the relief valve pressure setting of high pressure relief valve (1). The correct pressure setting is 17230 ± 520 kPa (2500 ± 75 psi).

(1) High pressure relief valve (2) Low pressure relief valve (3) Hoist dual stage relief valve (6) Nut(7) Retainer



6. Loosen nut (6). Turn retainer (7) in order to adjust the setting of high pressure relief valve (1) .

7. When high pressure relief valve (1) is correctly set, tighten nut (6) .

Relief Valve Test (Low Pressure)

(8) Pressure tap

1. Lower the dump body. Stop the engine.

2. Connect a hose assembly with an 8T-0856 Pressure Gauge (0 to 6000 kPa (0 to 870 psi)) to pressure tap (8) .

3. Start the engine. Operate the dump body repeatedly until the temperature of the hydraulic oil is above 38°C (100°F).

4. Lower the dump body onto the truck frame.
   Note: The hoist control must be in the RAISE position before low pressure relief valve (2) can be measured. If the hoist control is in the LOWER position the Power Train Electronic Control Module will keep the hoist control valve in the SNUB position. Low pressure relief valve (2) can not be measured in this condition.

5. Move a magnet in front of the hoist control until the alert indicator on the dash turns on.

6. Run the engine at high idle and move the hoist control to the LOWER position.

7. Look at the gauge and hold the hoist control in the LOWER position. The high pressure gauge reading is the relief valve pressure setting. The correct pressure setting is 3450 ± 350 kPa (500 ± 50 psi).

(1) High pressure relief valve (2) Low pressure relief valve (3) Hoist dual stage relief valve (9) Retainer(10) Nut



8. Loosen nut (10). Turn retainer (9) in order to adjust the setting of low pressure relief valve (2) .

9. When low pressure relief valve (2) is correctly set, tighten nut (10) .

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769D Off-Highway Truck Hydraulic System: Hoist Cylinder Performance - Test & Relief Valve (Hoist Dual Stage) - Test and Adjust 2013-01-07T15:41:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown