The core working principle of an excavator's hydraulic system is "using hydraulic oil as the transmission medium, converting mechanical energy into hydraulic energy through power components, then converting hydraulic energy back into mechanical energy through actuating components, and finally realizing the precise movement of working devices (such as buckets, booms) or traveling mechanisms". In essence, it is a closed-loop system for "energy conversion and transmission". Its working process can be broken down into four key links: "power input → energy conversion → action execution → control and regulation", with the specific principles as follows:

1. Core Composition: The "Five Key Components" of the Hydraulic System

To understand the principle, it is first necessary to clarify the core components of the system—all movements rely on the coordinated work of these five types of components:

2. Working Process: The Complete Chain from "Stepping on the Throttle" to "Bucket Excavation"

Taking the most basic "bucket excavation" movement of an excavator as an example, the working process of the hydraulic system can be divided into 5 steps, which clearly reflect the conversion and transmission of energy:

1. Power Input: The engine drives the hydraulic pump to "generate pressure"
   After the excavator is started, the diesel engine (or electric motor) drives the hydraulic pump to rotate through a coupling. At this time, the volume of the "oil suction chamber" of the hydraulic pump expands, creating negative pressure, and hydraulic oil is sucked from the hydraulic oil tank through the oil suction pipe (the filter among the auxiliary components first filters impurities in the oil to avoid blocking the valve body). Subsequently, the volume of the "oil pressure chamber" of the hydraulic pump shrinks, pressurizing the sucked hydraulic oil to form "high-pressure oil" with a certain pressure and flow rate—this step completes the conversion of "mechanical energy → hydraulic energy".

2. Control and Regulation: The multi-way valve "distributes" high-pressure oil
   When the operator operates the "bucket control lever", the lever drives the spool inside the multi-way valve (the "hub" of the hydraulic system) to move, opening the channel of the corresponding oil circuit. After the high-pressure oil flows out of the hydraulic pump, it is accurately distributed by the multi-way valve to the rodless chamber of the "bucket cylinder" (the chamber on one side of the piston in the cylinder without a piston rod, which has a larger volume and stronger thrust), while closing other irrelevant oil circuits—this step determines "where the oil goes and how much goes there", and directly controls the direction and speed of the movement (the greater the movement amplitude of the spool, the larger the opening of the oil circuit, the more oil flow, and the faster the movement).

3. Action Execution: The hydraulic cylinder "exerts force" to drive the bucket
   After the high-pressure oil enters the rodless chamber of the bucket cylinder, it generates a huge thrust on the piston inside the cylinder (according to Pascal's Principle, pressure = thrust / area; the rodless chamber has a larger area, so the thrust is stronger under the same pressure), pushing the piston to drive the piston rod to extend. The piston rod is connected to the linkage mechanism of the bucket; when the piston rod extends, it pulls the bucket to rotate around the hinge point, and finally realizes the "bucket excavation" movement—this step completes the reverse conversion of "hydraulic energy → mechanical energy", converting hydraulic pressure into mechanical force and displacement.

4. Oil Return Cycle: Low-pressure oil "flows back" to the oil tank
   When oil enters the rodless chamber of the bucket cylinder, the hydraulic oil in the rod chamber (the chamber on the other side of the piston with a piston rod) is squeezed by the piston and becomes "low-pressure oil". The multi-way valve simultaneously opens the oil return channel of the rod chamber; the low-pressure oil flows through the cooler (reduces the temperature of the oil to avoid overheating) and the filter (filters impurities again) through the oil return pipe, and finally flows back to the hydraulic oil tank, completing a full cycle of "oil suction → oil pressure generation → work done → oil return".

5. Safety Protection: The relief valve "limits pressure" to prevent overload
   If the bucket encounters a hard object (such as a rock) during excavation, the cylinder will be subjected to excessive force, leading to a sharp increase in the pressure in the oil circuit. When the pressure exceeds the "set safety value" of the relief valve, the relief valve will open automatically, directly diverting the excess high-pressure oil back to the oil tank, preventing damage to the hydraulic pump, cylinder, or oil pipe due to overpressure—this is the core safety protection mechanism of the hydraulic system.

3. Core Principle Support: Pascal's Principle

The reason why the entire hydraulic system can realize "controlling large forces with small forces" and "precise force transmission" essentially relies on Pascal's Principle (hydrostatic transmission principle): In a closed static liquid, the pressure at any point is transmitted equally to all parts of the liquid in the same direction.

For example, the pressure generated by the hydraulic pump (assuming 20MPa) is evenly transmitted to every surface of the hydraulic cylinder. Since the area of the rodless chamber of the cylinder (assuming 100cm²) is much larger than that of the rod chamber (assuming 50cm²), according to the formula "thrust = pressure × area", the thrust of the rodless chamber (20MPa × 100cm² = 200kN) will be much greater than that of the rod chamber. This allows the bucket to easily excavate heavy materials—and this is also the key reason why excavators can "achieve great things with small inputs" and realize heavy-load operations.

Summary

The essence of an excavator's hydraulic system is "using hydraulic oil as the medium, realizing the two-way conversion of mechanical energy and hydraulic energy through components such as hydraulic pumps, multi-way valves, and hydraulic cylinders, and transmitting force and movement with the help of Pascal's Principle". Its advantages lie in: being able to transmit huge forces with a small structural volume, achieving stable movements and rapid responses, and accurately adjusting the movement speed by controlling the oil flow rate—perfectly adapting to the operational needs of excavators for "heavy-load excavation + precise control".

Would you like me to sort out a simplified English diagram description of the excavator hydraulic system workflow based on this translated content, so that you can more clearly understand the connection between each link of the system?