The excavator is the most common construction machine on any job site, but do you really understand how it works inside? A seemingly simple excavator actually consists of five core systems working in synergy. Understanding these systems can significantly improve both daily operations and fault diagnosis.

Power System: The "Heart" of the Excavator

All excavators are powered by diesel engines. The power output of engines currently used by mainstream brands ranges from 30 kW (small machines) to over 400 kW (ultra-large machines).

Key Parameters:

  • Displacement: Small machines typically 2–4L, medium machines 6–12L, large machines 15–25L
  • Speed: Rated speed generally 1800–2200 rpm
  • Emission Standards: China has fully implemented National IV standards, with some regions requiring National V

Taking the SANY SY75C as an example, it is equipped with an Isuzu 4JG3 engine with a rated power of 42.4 kW, meeting National IV emission standards. The engine connects directly to the hydraulic pump via the flywheel, converting mechanical energy into hydraulic energy.

Notably, electric excavators have been developing rapidly in recent years. SANY's electric excavator uses lithium battery packs to replace diesel engines, achieving zero emissions and reducing operating costs by approximately 70%. For electric excavator pricing information, please feel free to contact us.

Hydraulic System: The "Muscles" of the Excavator

The hydraulic system is the core of the excavator's execution capability. Simply put, the engine drives the hydraulic pump to generate high-pressure oil, which is distributed to various cylinders and motors through control valves to drive the movement of working devices.

Three Core Components:

Hydraulic Pump: Converts the engine's rotational energy into hydraulic energy. The mainstream types are gear pumps (low cost, suitable for small machines) and piston pumps (high efficiency, variable control)

Control Valve: Controls the direction and flow of hydraulic oil. Pilot-operated control valves are currently the mainstream solution, offering lighter operation

Hydraulic Cylinders/Motors: Convert hydraulic energy into linear or rotational motion. Boom cylinders, arm cylinders, and bucket cylinders are the three core cylinders of an excavator

Operating Principle Summary: The operator pushes the pilot control lever → pilot oil pushes the main valve spool → high-pressure oil enters the hydraulic cylinder → cylinder extension/retraction drives the working device movement. The entire process response time is typically within 0.3 seconds.

Compared to wheel loaders, the hydraulic circuit of an excavator is more complex because it must simultaneously control three independent operations: swing, travel, and working device.

Working Device: The "Arms" of the Excavator

The working device is the part of the excavator that directly contacts materials. It consists of three components: the boom, arm, and bucket, connected through articulated joints.

Different Types of Working Devices:

| Type | Application Scenario | Features |

|------|---------------------|----------|

| Standard | Earthwork excavation, backfill | Most common, highly versatile |

| Extended Arm | Deep foundation pits, river dredging | Large working radius, but reduced digging force |

| Demolition | Building demolition | Equipped with breaker hammer or grapple |

| Lifting | Equipment hoisting | Equipped with hook, suitable for light lifting |

For a 20-ton class medium excavator, under standard configuration, the maximum digging depth is approximately 6.5 meters, the maximum digging radius is approximately 9.8 meters, and the bucket capacity is 0.8–1.2 cubic meters.

Swing and Travel System: The "Legs and Feet" of the Excavator

The excavator's mobility comes from two parts: the swing mechanism and the travel mechanism.

Swing System:

  • Swing motor (hydraulic driven) + swing reducer + swing bearing
  • Medium machines typically have a swing speed of 8–12 rpm
  • 360-degree full swing is standard on excavators

Travel System:

  • Tracked: Low ground pressure, suitable for soft ground, most common on construction sites
  • Wheeled: High mobility, can travel on roads, suitable for frequent relocations

The travel movement of a tracked excavator is driven by two independent travel motors that separately drive the left and right tracks, with turns achieved through differential speed. Travel speed is typically 3–5 km/h, slightly faster than walking speed.

Electronic Control System: The "Brain" of the Excavator

The electronic control system of modern excavators has evolved from simple instrument displays to intelligent management platforms.

Core Functions:

  • Engine Management: ECU controls fuel injection quantity and speed, enabling automatic idle
  • Hydraulic Management: Automatically adjusts pump output flow based on load, achieving 15–20% energy savings
  • GPS Positioning: Remote monitoring of equipment location, working hours, and fuel consumption
  • Fault Diagnosis: Real-time monitoring of sensor data with alarms for abnormalities

Taking the XCMG XE215DA as an example, it is equipped with an intelligent control system that can automatically match engine and hydraulic power based on working conditions. The operator only needs to focus on the digging action while the system automatically optimizes efficiency.

Selection Guide: Matching the Right System to Your Working Conditions

Choosing an excavator involves more than just looking at tonnage — you need to consider the compatibility of the five major systems based on specific working conditions:

  • Primarily Earthwork: Prioritize hydraulic system efficiency and engine fuel consumption
  • Primarily Breaking Operations: Focus on hydraulic system pressure and working device strength
  • Frequent Relocations: Wheeled excavators or small tracked machines are more suitable
  • Strict Environmental Requirements: Consider electric or National V and above emission models

For full product line pricing information, please contact our sales team. We will recommend the most suitable model based on your specific working conditions.

Conclusion

The five major systems of an excavator may appear independent, but they are actually closely interconnected. The engine provides power, the hydraulic system transmits energy, the working device executes actions, the travel system provides mobility, and the electronic control system coordinates everything. Understanding these principles not only helps operators use equipment more effectively but also provides a technical foundation for daily maintenance.

The construction machinery industry is undergoing a transformation from mechanization to intelligence. Electrification, unmanned operation, and intelligentization will become the main themes of future development. Follow EquipNode for more industry frontier news and technical insights.