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.

Proper installation is critical for performance and longevity.

• Filtration: Install a precision filter with a rating of 5 microns or less upstream of the servo valve. The hydraulic fluid cleanliness should be maintained at a maximum ISO DIS 4406 Code 16/13, with Code 14/11 recommended.
• System Flushing: Before installing the servo valve, the entire hydraulic system must be thoroughly flushed to remove contaminants. Use a flushing manifold and circulate fluid under conditions simulating normal operation.
• Mounting: The valve can be mounted in any orientation, ensuring port alignments match the manifold. The mounting surface should be clean, smooth, and flat. Use the specified screws and torque them to 96 inch-pounds.
• Connections: Use O-ring seal connections (e.g., SAE J1926) and avoid welded fittings. Prefer crimped or 24-degree cone type connections.

Common faults can be categorized as follows:

• Electrical Faults: Include power supply failure, cable damage, or poor contact. Check the supply voltage, cables, and connectors.
• Mechanical Failures: Such as a stuck valve spool, damaged springs, or worn seals. Regular inspection, cleaning, lubrication, and part replacement are necessary.
• Hydraulic Faults: Including oil contamination, low oil level, or oil leaks. Regularly replace and filter the oil, check oil levels, and repair leaks.
• Valve Oscillation: Unstable operation may be caused by issues with the servo valve's resolution, wear of the valve port, or incorrect control system parameters.