A Vickers servo valve is a type of control valve that is used to regulate the flow of fluid in a hydraulic or pneumatic system. It typically consists of a valve body, a servo piston, and an actuator. 

The servo piston is connected to an external control signal, such as an electrical signal from a controller, which is used to adjust the position of the valve. 

The actuator converts the control signal into a mechanical movement, which opens or closes the valve to control the flow of fluid. 

Vickers servo valves are commonly used in industrial and mobile applications, such as construction equipment, manufacturing, and aerospace. They are known for their high accuracy, fast response times, and durability.