I. Basic Working Principle of the Hydraulic System

The hydraulic system in an excavator is a closed-loop power transmission system. Its core principle is:
Engine mechanical energy → Hydraulic pump converts it to hydraulic energy → Control valve distributes flow → Actuators (cylinders/motors) execute motion → Mechanical action is completed.

Workflow:

1. Power Input: The engine drives the hydraulic pump (e.g., piston pump), converting diesel's chemical energy into hydraulic pressure.

2. Pressure Output: High-pressure oil flows through the main control valve (multi-valve block) to actuators (boom/arm/bucket cylinders, swing motor, travel motors).

3. Motion Control: Operator joysticks use pilot pressure (low-pressure oil) to shift the main valve spool, regulating oil flow direction and speed for precise movements.

4. Return Cycle: Low-pressure oil returns to the tank, is filtered, and re-enters the pump.

II. 6 Key Components of the Hydraulic System

1. Hydraulic Pump (Power Source)

• Types:

• Piston pump (most common): High-pressure, high-efficiency (used in medium/large excavators).

• Gear pump: Low-cost, used in small excavators or pilot systems.

• Function: Converts engine rotation into hydraulic pressure (typical working pressure: 20-35 MPa).

2. Main Control Valve (Multi-Valve Block)

• Role: Distributes oil flow to control actuator sequence and speed.

• Advanced Tech:

• Load-sensing valves: Auto-adjust flow based on demand (saves 15%+ fuel).

• Electro-hydraulic proportional valves (smart excavators): Enable precise electronic control.

3. Hydraulic Actuators

• Cylinders:

• Boom cylinder (lifts arm), arm cylinder (extends/sticks), bucket cylinder (controls bucket tilt).

• Hydraulic Motors:

• Swing motor: Rotates the upper structure 360° (with brake).

• Travel motor: Drives tracks (often with gear reduction).

4. Pilot Control System

• Function: Uses low-pressure oil (3-5 MPa) to move main valve spools, allowing smooth joystick operation.

• Key Parts: Pilot pump (gear pump), pilot valve (joystick-linked), pilot filter.

5. Hydraulic Tank & Auxiliary Components

• Tank: Stores oil, dissipates heat, and traps contaminants (equipped with level gauge and breather).

• Filters:

• Suction filter (protects pump), return filter (cleans oil).

• Cooler: Prevents overheating (>80°C degrades oil rapidly).

6. Safety & Regulation Devices

• Relief valve: Limits max system pressure (prevents component damage).

• Counterbalance valve: Prevents boom/arm free-fall due to gravity (critical for safety).

• Accumulator: Absorbs pressure shocks (essential for breaker attachments).

III. Evolution of Hydraulic Systems

IV. Common Failures & Maintenance Tips

• Slow/Weak Movements:

• Check pump wear, valve blockages, or cylinder leaks.

• Overheating:

• Clogged cooler, contaminated oil, incorrect pressure settings.

• Noise/Vibration:

• Air in the system (bleed or replace oil).

Maintenance Recommendations:

• Replace hydraulic filters every 500 hours, oil every 2000 hours (varies by workload).

• Inspect cylinder rod seals regularly to prevent dust damage.

V. Summary

The hydraulic system is like the "circulatory system" of an excavator:

• Heart: Hydraulic pump (power generation).

• Veins: High-pressure hoses (energy transfer).

• Limbs: Cylinders/motors (motion execution).

• Brain: Control valves (precision coordination).

Understanding these components improves operating efficiency, reduces downtime, and guides maintenance decisions.