The servo valve in a hydraulic system is a precision control element that converts electrical or mechanical signals into hydraulic energy output. Its core function is to achieve high-precision, fast-response fluid control. The following is a detailed analysis of the definition, working principle, classification, and function of the servo valve:

1. Definition and Basic Structure of a Servo Valve

A servo valve is a core component of an electro-hydraulic servo system. It receives a weak electrical signal (such as current or voltage) to actuate the valve core, thereby precisely regulating the flow, pressure, and direction of the hydraulic fluid. Its main components include:

① Electro-mechanical converter:

Such as a torque motor or force motor, it converts the electrical signal into mechanical motion (such as the displacement of a flapper or valve core).

② Hydraulic amplifier:

Typically composed of a pre-stage (such as a nozzle flapper or jet tube) and a main valve stage, it amplifies hydraulic energy.

③ Feedback mechanism:

Such as a linear variable differential transformer (LVDT) or a mechanical feedback lever, it ensures that the valve core position is consistent with the input signal.

2. Working Principle of Servo Valve

(1) Signal Conversion

The input electrical signal drives the torque motor to generate a magnetic field, which drives the flapper or jet tube to deflect, changing the pressure distribution of the pre-stage oil circuit.

Example: In a nozzle-flapper servo valve, the flapper offset causes a pressure difference between the nozzles on both sides, pushing the main valve core to move.

(2) Hydraulic Amplification

The tiny displacement of the pre-stage is amplified by the main valve core, controlling the flow of high-pressure oil to the actuator (such as a hydraulic cylinder or motor).

(3) Closed-loop Feedback

The valve core displacement is fed back to the controller through sensors such as LVDT, forming a closed-loop control to correct errors and ensure that the output and input signals are linearly matched.

3. Classification of servo valves According to the structure and working principle, servo valves can be divided into the following categories:

(1) Nozzle baffle type

Simple structure, fast response, easily affected by oil contamination, high-precision positioning system (such as machine tools)

(2) Jet tube type

Uses jet deflection to control flow, has strong anti-pollution ability, and is suitable for complex working conditions, engineering machinery, aerospace

(3) Sliding valve type

Directly adjusts flow through valve core displacement, with high control accuracy, but high friction and heavy hydraulic system

(4) Force feedback type

The force feedback mechanism improves stability. The structure is complex but the control accuracy is extremely high. It is suitable for precision force control systems (such as robots).

4. Functions of servo valves

(1) Precise control of fluid parameters

① Regulate the flow, pressure and direction of hydraulic oil to achieve high-precision control of the position, speed and force of the actuator.

② For example: in a hydraulic straightening machine, the servo valve controls the movement accuracy of the hydraulic cylinder by dynamically adjusting the flow (error <0.1mm).

(2) Power amplification:

amplify the microwatt-level electrical signal to a kilowatt-level hydraulic power output to drive a large load.

(3) System protection and safety

① Limit the risk of overpressure and prevent equipment overload by quickly closing the oil circuit.

② Detect anomalies (such as excessive oil temperature) and trigger shutdown protection.

(4) Energy saving and efficiency improvement

Dynamically adjust the flow to reduce energy waste. For example, in an injection molding machine, energy consumption can be reduced by more than 30%.

5. Typical application areas

(1) Aerospace:

High-response hydraulic drive of flight control servos.

(2) Industrial automation:

Force control and precise positioning of robot joints.

(3) Energy equipment:

steam turbine speed control systems, wind turbine pitch control.

(4) Engineering machinery:

coordinated control of complex motions in excavator arms.

6. Summary

Servo valves achieve high precision, high response, and intelligent hydraulic systems through electro-hydraulic conversion and closed-loop control, and are an indispensable core component of modern industrial equipment. Their performance optimization (e.g., valve core structure design) and enhanced anti-interference capabilities (e.g., redundant sensors) are key areas for future development.