Description The servovalves D761 Series consist of an electromechanical transformer (torque motor), a hydraulic amplifier (nozzle/flapper principle), a spool in a bushing and a cantilever feedback spring. The torque motor contains coils, pole pieces, permanent magnets and an armature.

The armature is connected to a flexible tube which allows a limited rotation of the armature and at the same time seals the electromagnetic components against the hydraulic fluid. The hydraulic amplifier is a full bridge arrangement with two upstream fixed orifices and two downstream variable orifices created by two nozzles and a flapper between them. The flapper is connected at its upper end to the centre of the armature and extends downward through the flexure tube to the nozzles. A deflection of the flapper between the nozzles changes the size of the variable orifices in opposite sense.

The 4-way spool controls fluid flow from pressure port to one of the load ports and also from the other load port to return. Deflection of the feedback spring due to spool displacement produces a torque which is fed back to the torquemotor.

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