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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock. |
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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 work tools have been lowered to the ground, and the 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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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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Right main control valve (rear view) (1) Lower line relief valve | |
The line relief valve (lower) is located on the rear side of the right main control valve. The line relief valve (lower) relieves pressure in the rod end circuit of the lift cylinders when the main control valve is in the HOLD position. The line relief valve protects components of the lift circuit from high pressure. External loads on the bucket may cause these high pressures.
A hydraulic test bench is the most accurate method for testing line relief valves. If it is not practical to use a test bench, then use the following procedure on the machine.
Reference: For the pressure and flow for bench testing this valve, refer to the Service Manual module Specifications, "Relief Valve (Line)" for the machine that is being serviced.
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The line relief is set higher than the main relief. Do not increase the main relief setting to check the line relief setting. Damage to the hydraulic system may result. |
- Connect Caterpillar ET to the machine. The ET connector is located on the control panel on the right side of the cab.
- Turn the engine start switch to the ON position.
- Open the ET software program.
- When ET has started, start the engine. Run the engine at high idle. Warm the hydraulic oil to normal operating temperature.
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Illustration 2 g01447460 - Select "Implement 993K". Press the "OK" button.
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Illustration 3 g01447462 - Select "Diagnostic Tests" from the "Diagnostics" menu. Select "Cylinder End Line Relief Pressure Tests".
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Illustration 4 g01447484 - When the dialog box appears on the screen, read the information in the dialog box. In order to continue with the test procedure, select the "OK" button.
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Illustration 5 g01447490 - When the dialog box appears on the screen, four checked boxes appear. Leave the check mark in the box for each test that will be performed. Select the "Begin" button in order to start the procedure.
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Illustration 6 g01447346 - Press the "Next" button in order to begin the procedure. Follow the instructions on the screen. A check mark will appear next to each step as each step is completed.
- Make sure that the area around the machine is level and clear of obstacles. Keep all personnel away from the machine. Press the "Next" button.
- Engage the parking brake.
- Lower the work tool to the ground. Press the "Next" button.
- Place the steering frame lock in the LOCKED position. Press the "Next" button.
- Turn the engine start switch to the OFF position.
- Place the hydraulic lockout switch in the LOCKED position. Press the "Next" button.
- Adjust the lower line relief valve.
- Loosen the locknut on the valve.
- Turn the adjustment screw by two complete turns in the counterclockwise direction.
- Tighten the locknut.
- Start the engine. Ensure that the parking brake is engaged.
- Engage the transmission lockout.
- Place the hydraulic lockout switch in the UNLOCKED position.
- Warm the hydraulic oil to a temperature of
43 °C (109 °F) or higher. Press the "Next" button.Show/hide table
Illustration 7 g01447351 - Place the tilt control lever in the TILT BACK position until the bucket is fully racked.
- Place the lift control lever in the LOWER position until the linkage is fully lowered.
- Run the engine at low idle.
- Ensure that the lift control lever and the tilt control lever are in the HOLD position. Press the "Next" button.
- Place the lift control lever in the LOWER position. Hold the lever in the LOWER position until the check mark appears on the screen.
- Place the lift control lever in the HOLD position. Press the "Next" button.
- Lower the bucket until the bucket rests flat on the ground. Press the "Next" button.
- Turn the engine start switch to the OFF position.
- Place the hydraulic lockout switch in the LOCKED position. Press the "Next" button.
- If the measured pressure was within the specification, ET will proceed to Step 32. If the pressure was not within the specification, proceed to the next step.
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Illustration 8 g01447369 - A dialog box will appear. The box will indicate that the measured pressure is not within the specification. Adjust the lower line relief valve. Follow the instructions in the dialog box. After adjusting the valve, press the "OK" button. ET will return to Step 19.
- If the measured pressure is within the specification, reset the lower line relief valve.
- Loosen the locknut on the valve.
- Turn the adjustment screw by two complete turns in the clockwise direction.
- Tighten the locknut.
- Turn the ignition key to the ON position. Press the "Next" button.
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Illustration 9 g01447376 - When the procedure is complete, the "Service Test Successful" message will appear on the screen. In order to exit the program, select the "Finish" button.
- Turn the engine start switch to the OFF position. Disconnect ET from the machine.
