The D765 Series flow control servovalves are throttle valves for 3- and preferably 4-way applications. The design of these valves is based on the well known 760 and D761 Series.The mechanical feedback has been replaced by a position transducer for electrical feedback. Integrated electronics close the position loop for the main spool. These valves are suitable for electrohydraulic position, speed, pressure or force control systems with high dynamic response requirements.

Principle of operation An electrical command signal (flow rate set point) is applied to the integrated position controller to the torque motor coils, and creates a magnetic force which acts on the ends of the pilot stage armature This causes a deflection of armature/flapper assembly within the flexure tube. Deflection of the flapper restricts fluid flow through one nozzle, which is carried through to one spool end, displacing the spool.

Movement of the spool opens the supply pressure port (P) to one control port while simultaneously opening the tank port. The position transducer (LVDT), which is excited via an oscillator, measures the position of the spool ( actual value, position voltage).The signal is then demodulated and fed back to the controller where it is compared with the command signal.The controller drives the pilot stage until the error between command signal and feedback signal will be zero. Thus, the position of the main spool is proportional to the electrical command signal.

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