The hydraulic system is the core power transmission system of an excavator, directly affecting its operational efficiency and reliability. Below is a detailed explanation of the hydraulic system's working principles and troubleshooting methods for common failures.

1. Basic Components of the Hydraulic System

• Hydraulic Pump (Main Pump, Pilot Pump)
  Converts mechanical energy (engine power) into hydraulic energy, delivering high-pressure oil.

• Control Valve (Main Control Valve, Multi-Valve Block)
  Distributes hydraulic oil flow to actuators (cylinders, motors).

• Actuators

• Hydraulic Cylinders (Boom, Arm, Bucket) – Perform linear motion.

• Hydraulic Motors (Travel, Swing) – Perform rotational motion.

• Hydraulic Tank & Filters
  Stores oil, dissipates heat, and filters contaminants to protect the system.

• Pilot Control System
  Uses low-pressure oil to operate main valves, reducing operator effort.

2. Working Principle of the Hydraulic System

① Power Transmission Flow

Engine → Hydraulic Pump → Main Control Valve → Actuators (Cylinders/Motors) → Action Execution

• Main Pump: Typically a variable-displacement piston pump that adjusts flow and pressure based on load.

• Main Control Valve: Distributes oil to different cylinders/motors based on joystick signals.

• Pilot System: Joystick sends low-pressure signals to shift main valve spools.

② Key Action Example (Bucket Digging)

1. Operator moves right joystick (pilot oil flows) → Main valve spool shifts.

2. High-pressure oil enters the bucket cylinder’s rod side → Piston retracts → Bucket closes for digging.

3. Return oil passes through filters for cooling before returning to the tank.

3. Common Hydraulic Failures & Troubleshooting

① Slow or No Movement

Possible Causes:

• Worn hydraulic pump (low output pressure).

• Sticking or leaking main control valve.

• Low pilot pressure (normal: 3–5 MPa).
  Troubleshooting Steps:

1. Check pilot pressure.

2. Test main pump outlet pressure (standard: 30–35 MPa).

3. Isolate cylinders/motors to identify internal leaks.

② High Oil Temperature (>80°C)

Possible Causes:

• Degraded/contaminated oil.

• Clogged cooler or faulty fan.

• Excessive system pressure.
  Troubleshooting Steps:

1. Inspect oil level and quality (dark/foamy oil = replace).

2. Use an IR thermometer to locate overheating components.

③ Uncoordinated Movements (e.g., Uneven Travel)

Possible Causes:

• Worn travel motor distribution plate.

• Sticking main valve spool.

• Hydraulic leaks (check cylinder seals).
  Troubleshooting Steps:

1. Swap left/right travel motor hoses to confirm motor failure.

2. Compare pressure readings for both sides.

④ Abnormal Noises (Pump Whining)

Possible Causes:

• Pump cavitation (low oil level/air leaks).

• Air bubbles in oil (clogged return filter).

• Damaged pump bearings.
  Troubleshooting Steps:

1. Check oil level and suction filter.

2. Listen for noise sources (pump noise often accompanies vibration).

⑤ Cylinder Drift (Boom Drops)

Possible Causes:

• Worn cylinder seals.

• Internal valve leaks.

• Overload valve failure.
  Troubleshooting Steps:

1. Raise the boom, shut off the engine, and observe drift speed (>5 minutes = normal).

2. Disassemble the cylinder to inspect piston seals.

4. Hydraulic System Maintenance Tips

• Replace hydraulic oil and filters regularly (every 2,000 hours or per OEM).

• Monitor oil temperature (normal range: 50–70°C).

• Avoid prolonged overloading to prevent pump/valve wear.

• Release hydraulic pressure before shutdown (operate joysticks to depressurize).

5. Troubleshooting Tools

• Pressure Gauge: Checks pump/valve pressure.

• Flow Meter: Measures pump output.

• IR Thermometer: Identifies overheating parts.

• Stethoscope: Pinpoints noise sources.

Conclusion:
Most hydraulic failures stem from contamination, wear, or pressure imbalances. Systematic troubleshooting (pump → valves → actuators) minimizes downtime!