At Moog, we have been producing electro-hydraulic servo valves since 1951. Our experts have had countless discussions with our customers about their applications and how to use our valves to achieve the best performance for their applications. We have written a guide to deal with topics that are essential for making the best use of our valves.
Below is an interactive portion of our guide covering the operating principles of our valves. You can download the full guide that includes this material, as well as valve sizing, valve types, practical considerations when designing EH control systems, and routine maintenance information.
Nozzle flapper operated valves are piloted by a hydraulic amplifier that is actuated by a torque motor. We will start by describing the functional principle of a torque motor. Then we will explain the nozzle flapper hydraulic amplifier, and finally we will show you the function of a nozzle flapper piloted servo valve with mechanical spool position feedback.
Valve responding to change in electrical input
Valve condition following change
D661 valve in center position
D661 valve in open position P - > B
When a current is applied to the coil with one polarity, the flux in one of the air gaps surrounding the magnets is increased, cancelling out the flux in the other.
This unequilibrium allows the armature to move in the direction of the stronger magnetic flux.
The armature is moved in the opposite direction by changing the polarity of the current in the coil.
D684 valve in center position
D684 valve in open position P - > B