PL61 Pipelayer and D6K Track-Type Tractor Caterpillar

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Sudden movement of the machine or release of oil under pressure can cause serious injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the hydraulic system.

Problem List for the Hydraulic System

1. The temperature of the oil is too hot.

2. The pump makes unusual noise and the cylinder rods do not move smoothly.

3. A large amount of air is in the oil.

4. The pump standby pressure is too low.

5. The pump standby pressure is too high.

6. There is a pause before the pressure is reached in all circuits.

7. Any of the implements move, when the control lever is in the HOLD position.

8. The line relief valves are too noisy.

9. There is too much implement drift.

10. The implement droops, when the implement is moved from a partially raised position to a raised position.

11. All implement cycle times are too slow.

12. The cycle time for the lift cylinders, the cycle time for the tilt cylinder, the cycle time for the angle cylinder, or the cycle time for the auxiliary valve 1 cylinder is too slow.

13. There is a long pause when the blade enters the ground during the blade lower.

14. The cycle time for the lift cylinders, the cycle time for the tilt cylinder, the cycle time for the angle cylinder, or the cycle time for the auxiliary valve 1 cylinder is too fast.

Problem 1

The temperature of the oil is too hot.

Possible Causes

1. The oil level in the hydraulic tank is too low.

2. The viscosity of the oil is wrong or the wrong oil is used.

3. The pump is worn.

4. There is a restriction in flow due to a bent hose, a bent tube or a restriction in an oil passage.

5. There is air in a hydraulic circuit.

6. There is a restriction to the flow of air through the oil cooler.

7. The outside air temperature is too hot.

8. The piston seal on the pump is worn.

Problem 2

The pump makes unusual noise and the cylinder rods do not move smoothly.

Possible Causes

1. The oil level in the hydraulic tank is too low.

2. The viscosity of the oil is wrong.

3. There is a loose connection on the inlet side of pump or the tube on the pump outlet is bent.

4. The pump rotating group is worn.

5. There is air in a hydraulic circuit.

Problem 3

A large amount of air is in the oil.

Possible Causes

1. There is a loose connection on the inlet side of pump.

2. The hydraulic system was not purged of air after assembly, inspection or testing.

3. There is leakage in the cylinder seals or around the cylinder seals.

4. Check for loose fittings or cracked fittings.

5. The oil level in the hydraulic tank is too low.

6. There is aeration in the tank.

Problem 4

The pump standby pressure is too low.

Possible Causes

1. The flow compensator is set too low.

2. The spring for the flow compensator in the pump is broken.

3. The pump is not upstroking. The swashplate is blocked or the actuator spring is broken.

4. The signal network is blocked.

Problem 5

Pump standby pressure is too high.

Possible Causes

1. The flow compensator is set too high.

2. The flow compensator is not moving.

3. The load sensing relief valve is stuck or the load sensing valve is set too high.

4. The pump is not destroking. The actuator piston is stuck or the swashplate is blocked.

Problem 6

There is a pause before the pressure is reached in all circuits.

Possible Causes

1. The margin pressure is low.

2. There is air in the signal network.

3. There is leakage in the signal network.

4. An orifice is slightly plugged in the signal network.

Problem 7

Any of the implements move, when the control lever is in the HOLD position.

Possible Causes

1. The control valve spool or the bore for the valve spool may be worn excessively. This may cause leaks.

2. There is leakage in the seals or around the seals of the piston in the cylinders that are affected.

3. There is a leak in the lines between the control valve and the cylinders.

4. The solenoid for the control valve has current or the solenoid has contamination.

5. The makeup valves are open.

Problem 8

The line relief valves are too noisy.

Possible Causes

1. The line relief valves that are affected are set too low.

2. The springs in the line relief valves that are affected are broken or fatigued.

3. The pressure compensator valve is set too high.

Problem 9

There is too much implement drift.

Possible Causes

1. There is leakage in the seals or around the seals of the piston in the cylinder that is being affected.

2. The line relief valve is set too low.

3. There is leakage past the line relief/makeup valve in the circuit.

4. The spool in the main control valve is not correctly centered. This problem can be caused by a broken spring or a sticky valve spool.

5. The control valve spool or the bore for the valve spool may be worn excessively. This may cause leaks.

Problem 10

The implement droops, when the implement is moved from a partially raised position to a raised position.

Possible Causes

1. The signal passages in the main spool of the control valve that is affected is blocked.

2. The flow control spool is not operating properly.

3. The margin pressure is set too low.

4. There is air in the signal network.

Problem 11

All implement cycle times are too slow.

Possible Causes

1. There is a blockage or a leakage in the signal network.

2. The standby pressure is set too low.

3. The pump does not upstroke fully. The actuator piston is stuck or the swashplate is blocked.

4. The pump is worn.

5. The pressure compensator valve is set too low.

6. The pilot pressure is low.

7. The engine speed is too low.

Problem 12

The cycle time for the lift cylinders, the cycle time for the tilt cylinder, the cycle time for the angle cylinder, or the cycle time for the auxiliary valve 1 cylinder is too slow.

Possible Causes

1. The control valve spool is not fully shifted for the circuit that is affected.

2. The load signal to the pump compensator valve is blocked or partially blocked or there is leakage in the signal network.

3. The line relief valve for the affected circuit is set too low.

4. The line relief valve or the makeup valve for the affected circuit is leaking.

5. The seals for the cylinders are leaking for the affected circuit.

Problem 13

There is a long pause when the blade enters the ground during the blade lower.

Possible Causes

1. The makeup valve does not open.

Problem 14

The cycle time for the lift cylinders, the cycle time for the tilt cylinder, the cycle time for the angle cylinder, or the cycle time for the auxiliary valve 1 cylinder is too fast.

Possible Causes

1. The standby pressure is set too high.