Types of servo valves

A hydraulic servo valve is a device that measures the flow of oil in response to an electrical input signal to control the position, velocity, pressure or force through a piston in various machines. Servo valves are closed-loop control devices that can be single-stage, two-stage or three-stage.

Single-stage servo valve

Single-stage servo valves are used in open-loop systems with an approximate flow rate of up to 20 lpm. The low electrical signal input is directly applied to the hydraulic valve control spool, and it has no feedback circuits. Essential features of this valve include high dynamics, oil resistance, and ease of maintenance.

Two-stage servo valve

Two-stage servo valves are commonly used hydraulics to control the speed and direction. The two stages of this servo valve are the flapper nozzle system and servo spool system. It uses a torque motor control with a low electric powered signal.

Three-stage servo valve

Three-stage servo valves are used with closed-loop systems and have a flow rate greater than 150 to 200 lpm. The third stage is the main control. It is pilot controlled by a two-stage servo valve.

Flow control valves

Flow control servo valves are designed to produce hydraulic flow output proportional to the electrical current input.  These servo valves are available in:

Integrated digital electronics with optional fieldbus interface – these servo valves allow the technician to set operating parameters, activate the valve, and monitor its performance.

Analog interface with integrated electronics – these are servo valves that integrate the amplifier card and associated electronics into the valve body.

Analog interface without integrated electronics – these servo valves use external amplifier cards to convert an input signal to a control current that drives the servo valve torque motor.

Pressure and flow control

Pressure and flow control valves manage the flow and regulate pressure. They can be used for both pressure regulation and applying a pressure limit. Often, pressure and flow control valves contain integrated digital electronics with an optional fieldbus interface.

Servo valves and proportional valves with special features

Some servo valves and proportional valves have advanced safety features such as fail-safe and explosion-proof options and special performance modifications.

Contact Sealtec Hydraulics for details

Sealtec Hydraulics is the official distributor of star servo valves. In addition, we offer in-house repair of all types of servo valves, including Moog, Rexroth, Vickers, Parker, Abex, Denison Ext, and more.

To discuss how our hydraulic fitters and turners can assist you, get in touch with our team today.

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