TH220B, TH330B and TH340B Telehandlers Hydraulic System Hydraulic System Pressure - Release Caterpillar

Required Tools

Use the following tool when you remove the lock valve for the tilt cylinder.

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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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Cylinders equipped with load control valves can remain pressurized, even with hoses removed. Failure to relieve pressure before removing a load control valve or disassembling a cylinder can result in personal injury or death. Ensure all pressure is relieved before removing a load control valve or disassembling a cylinder.

Relieving Pressure in the Hydraulic System

Before you remove any hydraulic components from the machine make sure that all hydraulic pressure in the hydraulic system is relieved.

Before you start any maintenance on the boom, support the boom on a suitable stand. Refer to the "Tools and Shop Products Guide" for information on stands that are available.

1. Lower the work tool to the ground.

2. Shut off the engine.

3. In order to release any pressure from the hydraulic tank, you must loosen the hydraulic tank filler cap slowly.

4. Tighten the filler cap.

5. Relieve the system pressure from the lock valves and cylinders.

6. Relieve the system pressure from the shutoff valve and for the axle.

Location of the Load Control Valve (Lock)

Care must be taken when you are removing lock valves from the load control valve.

Lock valves are installed in the load control valves on the following cylinders:

• Telescoping Cylinder

• Boom Cylinder (Boom Raise/Lower)

• Tilt Cylinder

• Frame Leveling (If Equipped)

Illustration 1	g01000745
Load control valve for the telescoping cylinder (1) The lock valve is on the front side of the control valve.

Illustration 2	g01000501
Load control valve for the boom cylinder (boom raise/lower) (2) Lock valve

Illustration 3	g01013847
This is an example of the location for the load control valve and the lock valve for the tilt cylinder on the TH220B and the TH330B series machines.

Illustration 4	g01000875
Load control valve for the tilt cylinder (3) Lock valve

The lock valve for the tilt cylinder is a cartridge type valve. Lock valve (3) is located in the cartridge which is screwed directly into the cylinder.

Illustration 5	g01013263
Lock valve for the frame leveling cylinder (4) Lock valve

Relieving Pressure from the Load Control Valves (Lock)

The procedures in this section may be used in the following operations:

• Boom lowering without hydraulic power

• Boom retract without hydraulic power

• Maintenance on load control valves

• Maintenance on hydraulic cylinders

Note: For information regarding machine operation without hydraulic power, refer to Operation and Maintenance Manual, SEBU7708, "Equipment Lowering with Loss of Hydraulic Power".

The Following Procedure Should Be Used for the Telescoping Cylinder

Illustration 6	g01013334
Load control valve (1) Lock valve is on the back side of the control valve. (5) Adjusting screw (6) Locknut

1. Measure the distance from the head of adjusting screw (5) to the body of control valve. Record this measurement. This measurement will be required later when the adjusting screw (5) is reset.

2. Fully loosen locknut (6). Turn adjusting screw (5) as far as possible in a clockwise direction by hand.

3. Attach a wrench to adjusting screw (5) and turn adjusting screw (5) for an additional two full turns in a clockwise direction. The pressure must now be relieved from the implement control valve in order to release the pressure from the lock valve.

4. Refer to Operation and Maintenance Manual, SEBU7708, "Equipment Lowering with Loss of Hydraulic Power" for information on releasing the pressure from the implement control valve.

5. Reset the lock valve after all the pressure has been relieved. Refer to Operation and Maintenance Manual, SEBU7708, "Equipment Lowering with Loss of Hydraulic Power" for information on resetting the lock valve.

6. Loosen the lock valve slowly in order to release any pressure that remains in the lock valve. Ensure that all the hydraulic pressure is released from the lock valve before you remove the lock valve from the load control valve. Remove the lock valve from the load control valve.

The Following Procedure Should Be Used for the Boom Cylinder (Boom Raise/Lower).

Illustration 7	g01013338
Load control valve for the boom cylinder (2) Lock valve (7) Screw (8) Locknut

1. The lock valve is mounted to the underside of the cylinder, and toward the rear of the cylinder. The valve can be accessed from the underside of the machine.

2. Measure the distance from the head of adjusting screw (7) to the body of lock valve (2). Record this measurement. This measurement will be required later when adjusting screw (7) is reset.

3. Fully loosen locknut (8). Turn adjusting screw (7) as far as possible in a clockwise direction by hand.

4. Attach a wrench to adjusting screw (7) and turn adjusting screw (7) for an additional two full turns in a clockwise direction. The pressure in the lock valve will now be directed to the implement control valve. The pressure must now be relieved from the implement control valve in order to release the pressure from the lock valve.

5. Refer to Operation and Maintenance Manual, SEBU7708, "Equipment Lowering with Loss of Hydraulic Power" for information on releasing the pressure from the implement control valve.

6. Reset the lock valve after all the pressure has been relieved. Refer to Operation and Maintenance Manual, SEBU7708, "Equipment Lowering with Loss of Hydraulic Power" for information on resetting the lock valve.

7. Loosen the lock valve slowly in order to release any pressure that remains in the lock valve. Ensure that all the hydraulic pressure is released from the lock valve before you remove the lock valve from the load control valve. Remove the lock valve from the load control valve.

The Following Procedure Should Be Used for the Tilt Cylinder.

Illustration 8	g01017556
Lock valve for the tilt cylinder (9) Cap (10) Adjusting screw

The Following Procedure is for the Machine With A Two-Section Boom

1. Place the front coupler in a horizontal position and support the front coupler on the ground in order to ensure no movement of the function, when the lock valve is removed.

2. Remove cap (9) .

3. Turn adjustment screw (10) counterclockwise in order to relieve the pressure. Record the number of turns in order to reset the lock valve later. The adjusting screw should move out of the body of the lock valve. The pressure in the lock valve will now be relieved.

4. Reset the lock valve after all the pressure has been relieved.

5. The remaining residual pressure that is sustained within the spool will release in two to five minutes. Use the tool 242-0779 36 mm Deep Socket and loosen the lock valve slowly in order to release any pressure that remains in the lock valve. Ensure that all the hydraulic pressure is released from the lock valve before you remove the lock valve from the cylinder.

The Following Procedure is for the Machine With A Three-Section Boom.

1. Place the front coupler in a vertical position. The lower edge of the coupler should just clear the ground and hanging in the lowest position. This will take the load off the head end of the cylinder and the pressure should be relieved.

2. Remove cap (9) .

3. Turn adjusting screw (10) counterclockwise in order to relieve the pressure. Record the number of turns in order to reset the lock valve later. The adjusting screw should move out of the body of the lock valve. The pressure in the lock valve will now be relieved.

4. Reset the lock valve after all the pressure has been relieved.

5. Remaining residual pressure that is sustained within the spool will be released in two to five minutes. Use the tool 242-0779 36 mm Deep Socket and loosen the lock valve slowly in order to release any pressure that remains in the lock valve. Ensure that all the hydraulic pressure is released from the lock valve before you remove the lock valve from the cylinder.

The Following Procedure Should Be Used for the Frame Leveling Cylinder (If Equipped)

Illustration 9	g01027290

The following procedures should be used for the removal of the frame leveling valve.

1. Turn the wheels to a full LEFT position. This will allow access to the frame leveling valve.

2. Place a jack under the front axle. Raise the front wheels of the machine from the ground.

3. Place two stands under either end of the front plate of the chassis. Lower the chassis onto the stands. This will prevent the machine from tipping.

4. Support the wheel on the side of the axle with the frame leveling by placing a block under the wheel. This will help prevent any oil pressure that would be caused by the weight of the wheel.

5. Before you remove the hoses locate three plugs that will be used for plugging the hoses. Remove the three hoses that are connected to the valve (11). Plug the hose ends.

6. Disconnect the two solenoid connections. Mark the connections and the solenoids in order to make the correct connections during the installation of the new valve.

7. Carefully loosen the four bolts (12) that hold the valve down. Ensure that any oil that may leak is collected properly.

8. Continue to remove the four bolts and the valve.

9. Install a new valve.

10. Reconnect the hoses and the solenoid connections.

Verifying the Correct Setting of the Load Control Valves

The procedure for verifying the correct setting of the load control valves can be found in the following reference Operation and Maintenance Manual, "Equipment Lowering with Loss of Hydraulic Power".