An electrohydraulic servo valve is a precision component that acts as an interface between the electrical control system and the hydraulic power system. It receives a low-power electrical analog signal and converts it into a proportional, high-power hydraulic output (flow and pressure). This makes it a crucial control core in electrohydraulic servo systems, responsible for both electrical-to-hydraulic signal conversion and power amplification.

A Moog servo valve typically consists of a polarized electrical torque motor and a two-stage hydraulic amplifier.

• First Stage: The torque motor deflects an armature and a flapper attached to it. This flapper moves between two nozzles, creating variable orifices that control the pressure on either end of the second-stage spool.
• Second Stage: The differential pressure moves the spool, which then controls the flow of hydraulic fluid to the actuator. A feedback spring, connected to the flapper and engaging the spool, creates a force that balances the input signal torque, ensuring precise spool positioning proportional to the electrical command.