Beatrice Lang
The electro-hydraulic servo valve (EHSV) is a device that uses an electrical input signal to control the flow of a gas or liquid. It is a key component in electro-hydraulic servo control and is used in a wide range of industries, including aviation, aerospace, military defense, metallurgy, and the chemical industry. The development of the EHSV can be traced back to World War II, with advancements being made in the 1950s due to the adoption of permanent magnet torque motors. Today, companies such as Honeywell, Moog, Bosch Rexroth, and Parker Hannifin are known manufacturers of servo valves and related technologies.
| Characteristics | Values |
|---|---|
| First appearance | World War II |
| First two-stage servo valve | Used a solenoid to actuate a first-stage spool |
| Advancement | 1950s, due to the adoption of permanent magnet torque motors |
| Single-stage servo valve | Uses a torque motor to directly position a spool valve |
| Two-stage servo valve | May use flapper, jet pipe, or deflector jet valves as hydraulic amplifier first stages |
| Three-stage servo valve | May use an intermediate stage spool valve to position a larger third stage spool valve |
| Two-stage servo valve classification | Type of feedback used for the second stage (spool position, load pressure, or load flow feedback) |
| Jet pipe and nozzle flapper servo valves | Compete for similar applications that require high dynamics |
| Jet pipe valve | Used in a multistage configuration where mechanical feedback is replaced with electronic feedback |
| Multistage hydraulic valve | Usually, most designs do not exceed three stages |
| Nozzle flapper, jet pipe, or direct-driven valve | Satisfies most requirements for dynamics and flow |
| Manufacturers | United Kingdom Dowty, the United States Team, the United States Parker, Eaton Vickers, Germany Bosch, Rexroth, Moog, Danfoss' Controls Div., and others |
| Development trend | Design of a new structure, the use of new materials, and the combination of electronic, digital technology, and hydraulic technology |
| Advantages | Small size, compact structure, high power amplification coefficient, high control precision, good linearity, small dead zone, high sensitivity, good dynamic performance, and fast response |
| Use cases | Electro-hydraulic position, speed, acceleration, force servo system, servo vibration generator, aviation, aerospace, ship, metallurgy, chemical industry, blow molding, turbofan engine, fly-by-wire aircraft, industrial applications, military defense applications, automation, and a wide variety of other fields |
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What You'll Learn
History of the electro-hydraulic servo valve
The electro-hydraulic servo valve (EHSV) is a type of electrically-operated valve that controls the flow of hydraulic fluid to an actuator. EHSVs are often used to control powerful hydraulic cylinders with a small electrical signal, providing precise control of position, velocity, pressure, and force.
The EHSV was first developed during World War II, with the first two-stage servo valve using a solenoid to actuate a first-stage spool that drove a rotating main stage. However, these early EHSVs were characterised by poor accuracy and slow response times due to the challenges of rapidly converting electrical signals into hydraulic flows.
In the 1950s, advancements in EHSV technology were made with the adoption of permanent magnet torque motors as the first stage, replacing solenoids. This led to significant improvements in performance and response times. During this period, the MIT Dynamic Analysis and Control Laboratory invented the torque motor, which played a pivotal role in enhancing servo valve technology.
Over time, the development of EHSVs continued to progress, with manufacturers introducing various valve designs, including single flapper-nozzle valves, dual flapper-nozzle valves, and jet-pipe servo valves. In the 1990s, Parker, a manufacturer of jet tube servo valves, developed Voice Coil Drive technology (VCD) and DFplus control valves, further advancing the capabilities of EHSVs.
Today, EHSVs find applications in a diverse range of fields, including aviation, aerospace, military defence, industry, automation, and more. They are valued for their high precision, compact structure, fast response, and ability to control powerful hydraulic systems with minimal electrical signals.
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Single-stage servo valves
An electrohydraulic servo valve (EHSV) is an electrically operated valve that controls the flow of hydraulic fluid to an actuator. They are used to control powerful hydraulic cylinders with a small electrical signal. EHSVs are key components in electrohydraulic servo control systems, which are used in aviation, aerospace, shipping, metallurgy, and the chemical industry.
EHSVs first appeared during World War II, but were characterised by poor accuracy and slow response times. Advancements in EHSV technology took off in the 1950s, largely due to the adoption of permanent magnet torque motors as the first stage.
JASC is one manufacturer of single-stage servo valves. Their Clevis Servo Valve is used to meter fluid or for position control. It is capable of 2-way or 3-way operation and offers mechanical or electrical feedback. It also has low electrical power consumption, with a maximum requirement of 1.0 watts.
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Two-stage servo valves
Electro-hydraulic servo valves (EHSV) are electrically operated valves that control the flow of hydraulic fluid to an actuator. They are often used to control powerful hydraulic cylinders with small electrical signals. EHSVs are key components in electro-hydraulic servo control systems, which are used in aviation, aerospace, shipping, metallurgy, and the chemical industry.
EHSVs first appeared during World War II, but they were characterised by poor accuracy and slow response times. The first two-stage servo valve used a solenoid to actuate a first-stage spool, which in turn drove a rotating main stage. This design is similar to the servo valves used during the war, which also used a solenoid to drive a spool valve. The advancement of EHSVs took off in the 1950s, largely due to the adoption of permanent magnet torque motors as the first stage, as opposed to solenoids.
The development of new electro-hydraulic servo valve technology has been driven by the design of new structures, the use of new materials, and the combination of electronic, digital, and hydraulic technology. Moog servo valves are characterised by the fact that the valve spool is inserted into a bushing (spool-in-bushing), resulting in outstanding dynamics and excellent accuracy. Moog also produces proportional valves, where the valve spool is fitted directly into the valve housing (spool-in-body), making them particularly suitable for higher nominal volume flows.
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Three-stage servo valves
The electro-hydraulic servo valve (EHSV) is an electrically-operated valve that controls the flow of hydraulic fluid to an actuator. The EHSV first appeared during World War II, and its use continued into the 1940s. However, these early servo valves were characterised by poor accuracy and slow response times due to the inability to rapidly convert electrical signals into hydraulic flows.
The first two-stage servo valve used a solenoid to actuate a first-stage spool, which in turn drove a rotating main stage. The adoption of permanent magnet torque motors as the first stage in the 1950s greatly improved response times and reduced the power required to control the valves.
Manufacturers of servo valves include the United Kingdom's Dowty, the United States' Team and Parker, Germany's Bosch and Rexroth, and Honeywell, whose EHSV typically consists of two stages. Moog servo valves are also notable for their outstanding dynamics and excellent accuracy.
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Manufacturers of electro-hydraulic servo valves
Electro-hydraulic servo valves (EHSV) are electrically operated valves that control the flow of hydraulic fluid to an actuator. They are used in a variety of applications, including aviation, aerospace, automotive, manufacturing, and industrial machinery. The global market for EHSVs is growing due to the increasing demand for precise control in these industries.
Some of the manufacturers of EHSVs include:
- Honeywell: Honeywell is a leading manufacturer of EHSVs, which are part of their family of Electro-Mechanical Interface Devices (EMIDs). Their EHSVs are known for being compact, lightweight, and highly durable.
- Moog: Moog offers servo valves that provide high-precision control of position, velocity, pressure, and force in a wide range of applications.
- Parker: Parker has developed Voice Coil Drive (VCD) technology, which is used in their DFplus control valves. They have also acquired the original producer of jet tube servo valves, Abex United States.
- Dowty: Based in the United Kingdom, Dowty is another manufacturer of servo valves.
- Bosch: Bosch is a German manufacturer of EHSVs.
- Rexroth: Also based in Germany, Rexroth produces EHSVs.
These manufacturers play a crucial role in providing EHSVs to various industries, contributing to the growth and innovation in the electro-hydraulic servo valve market.
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Frequently asked questions
The electro-hydraulic servo valve was first developed during World War II. Advancements in the technology were made in the 1950s with the adoption of permanent magnet torque motors.
Manufacturers of electro-hydraulic servo valves include the United Kingdom's Dowty, the United States' Team and Parker, Germany's Bosch, and Rexroth, among others.
Electro-hydraulic servo valves are used in aviation, aerospace, military defence, industry, automation, shipping, metallurgy, and the chemical industry.
