G771K201A G77X/77XSeries flow control servo valves

The G77X/77XSeries Flow Control Servo Valve consistsof a polarized electrical torque motor and two stagesof hydraulic power amplification.The motor armatureextends into the air gaps of the magnetic flux circuit andis supported in this position by a flexure tube.The flexuretube acts as a seal between the electromagnetic andhydraulic sections of the valve.The 2 motor coils surroundthe armature, one on each side of the flexure tube.
The flapper of the first stage hydraulic amplifier is rigidlyattached to the midpoint of the armature.The flapperextends through the flexure tube and passes between 2nozzles, creating two variable orifices between the nozzletips and the flapper.The pressure controlled by the flapperand nozzle variable orifice is fed to the end areas of thesecond stage spool.

The second stage is a conventional four.way spool design inwhich output flow from the valve, at a fixed valve pressuredrop, is proportional to spool displacement from the nullposition. A cantilevered feedback spring is fixed to theflapper and engages a slot at the center of the spool.Displacement of the spool defects the feedback springwhich creates a force on the armature/flapper assembly.
Input signals induce a magnetic charge in the armatureand cause a deflection of the armature and flapper.Thisassembly pivots about the flexure tube and increases thesize of one nozzle orifice and decreases the size of theother.
This action creates a differential pressure from the one endof the spool displacement causing a force in the feedbackwire which opposes the original input signal torque. Spoolmovement continues until the feedback wire force equalsthe input signal force.