Hydraulic valves are of different types that are dedicated to performing various applications. The major applications include controlling the flow, rerouting flow direction, and pressure regulations. The simplest working of a valve is just opening/closing for starting or stopping fluid flow through the system. But, any failures to these hydraulic valves will affect the accuracy and control of the entire hydraulic system. The general types of hydraulic valves will be familiar to you. But, you can learn details on hydraulic servo valves here.
Normally, the hydraulic servo systems are used for efficiency, repeatability, and for obtaining accurate outputs. The primary functions of the hydraulic servo systems include monitoring, feedback, and correction. Most of the machine tool applications use hydraulic servo valves for accurate position control.
Hydraulic servo valve is a continuously acting directional control valve that converts the digital input varying from 0-max to an accurate hydraulic output. Servo valves are high-performance devices that require an electrical input signal for controlling the flow. The low electrical signal input for the servo valve can precisely control powerful hydraulic cylinders. Since servo valves use electric power, they are also called an electro-hydraulic servo valve.
The electro-hydraulic servo valves are more beneficial in closed-loop piping systems than ordinary valves. There are numerous other valve types that can be used as an alternative for servo valve systems. But, the electrically operated servo valves are more efficient and accurate. Also, this valve eliminates the time-consuming and risky process of manual operations that requires the contact of extreme quantities of fluids that operate under high pressure and temperature.
Let’s discuss some information on the working of hydraulic servo valves. Similar to all other valves, the fluid passing through the system is responsible for the valve or actuator movements. But, hydraulic servo valve operation differ with its mode. That is, hydraulic servo valve transfers a low-powered electrical input signal using a digital control panel for controlling the entire fluid flow. Then, the amplifier boosts this electrical signal strong enough to move the valve.
Flapper nozzle, torque motor and one or more spools are the important components of the hydraulic servo valve. When the low electrical signal is applied to the coil, the flapper will move by varying the nozzle opening as a result of electromagnetic force acting on both sides of the flapper. This flapper position will control the pressure in the system.
Also, Read: Types of Flow Control Valve
Types of Electro-Hydraulic Servo Valves
Single Stage Servo Valve
Single-stage servo valves are used in open-loop systems with an approximate flow rate up to 20 lpm. The low electrical signal input is directly applied to the hydraulic valve control spool and it has no feedback circuits. High dynamics, oil resistance, ease of maintenance, etc… are the important features of this valve.
Two-Stage Servo Valve
Two-Stage Servo valve the commonly used hydraulic servo valve that can be used for controlling the speed and direction. Flapper nozzle system and servo spool system are the two stages of this type of servo valve. This valve uses a torque motor control with a low electric powered signal. Also, this valve is used with the closed-loop system providing feedback.
Three-Stage Servo Valve
Three-stage servo valves are used with closed-loop systems having a flow rate greater than 150 to 200 lpm. In this, the third stage is the main control that is pilot controlled by a two-stage servo valve.