In hydraulics – that is, the applied science that deals with the mechanical properties of liquids – a valve is a device that is used to control liquid flow. Valves are used to stop or start the flow, tell the flow which direction to go, increase or decrease its speed, and release or regulate the pressure created by the flow.

There are many types of valves, but in the simplest terms, you can see the valves opening and closing in the accompanying hand pump illustration by Michael Frey from

Simple manual valves like those shown in the illustration are fine for low precision work. However, there are pipe systems that require a high degree of accuracy when it comes to controlling liquid flow. When high degrees of precision are needed, engineers often use servo valves to provide it.

A servo valve is a high-performance device for manipulating sophisticated pipe systems.

In sophisticated piping systems, it’s not always possible to handle valves manually. Doing so does not guarantee accuracy, and the flow may be too much to manage by hand. Manual control can also potentially be time-consuming and dangerous when using extreme quantities, pressures, temperatures, or chemicals.

Servo valves make managing piping systems, particularly closed-loop systems, much easier and more efficient. That is because they work using electrical signals and are operated remotely.

How does a servo valve work?

The process is actually quite simple. When you need to change the flow inside a particular piping system, whether to stop or start it, reroute it, change the pressure or modify its velocity, all you need to do is to send a low-powered electrical signal to the appropriate servo valve in your system using a digital control panel.

This low-powered signal goes through an amplifier, which boosts the signal until it becomes strong enough to change the position of the servo valve. The servo valve then manipulates the actuator (the equivalent to a simple kind of hand wheel) into carrying out the changes you want to see happen with the flow. And because the system is closed-loop, feedback is directed to the servo valve. This feedback enables the servo valve to generate a more accurate response to the received command.

Servo valves are used wherever a high degree of accuracy and control is required.

Servo valves are designed with accuracy and control in mind, and are often installed in systems that require efficiency. Applications for servo valves include regulating fluid flows at hydroelectric power plants and sites for mining gas or oil; regulating fuel flow in aircraft engines; and blow molding or the manufacture of hollowed plastic.

Additionally, since the workload on servo valves is great, they are typically expensive. Many engineers opt to use proportional valves instead of servo valves if they have calculated that they don’t really need the kind of accuracy and detailed output that servo valves provide. Also, on a case-to-case basis, the expense involved in purchasing new servo valves causes many engineers to seek out servo valve repair services when their servo valves fail.

Should You Purchase A New Hydraulic Servo Valve, Or Fix Your Old One? Let us help you decide.