Servo Valve
How does a servo valve differ from a proportional valve?
Servo valves use closed-loop internal feedback for ultra-fast response and very high precision, whereas proportional valves typically use external electronic feedback and offer moderate to high precision with slower response times.
What is the primary function of the electromagnetic driver?
It converts the electrical current into a small deflection proportional to the signal, which then moves the metering section to regulate output flow.
Why are direct-drive servo valves considered more reliable?
They cancel the intermediate transmission link, avoiding hysteresis and reducing mechanical wear by relying on system drive precision, thus improving electromechanical reliability.
What is the critical maintenance requirement?
Maintaining fluid cleanliness ≤5 microns and performing specialized maintenance by experts, as they require more maintenance than proportional valves due to their sensitivity.
A servo valve (electrohydraulic servo valve or EHSV) is a high-precision directional control valve that converts low-power electrical signals into mechanical motion to precisely regulate hydraulic fluid flow and pressure to an actuator, enabling closed-loop control of position, velocity, or acceleration.
On the shop floor, servo valves are deployed in closed-loop electrohydraulic motion control systems for applications requiring ultra-fast response and very high precision, such as CNC machinery, material testing simulators, plastics molding, and gas turbine engine fuel metering. They require fluid cleanliness of 5 microns or less and are coupled with sensors like LVDTs to provide continuous feedback for accurate process control.
Contamination-induced failure: Fluid exceeding 5 microns causes spool jamming, wear, or erratic response.
Leakage via clearance wear: Leakage between spool and sleeve is the main failure mode, leading to loss of pressure control and positioning accuracy.
Hysteresis and stiction: Poor maintenance of the electromechanical driver or intermediate links causes delayed response and positioning errors; direct-drive designs minimize this.