Hydraulic pilot stage in continuously adjustable valves for converting the mechanical output signal from the electrical input stage into an amplified hydraulic signal (Figure D 87).
- Armature and flapper are firmly connected together and are supported by a thin-walled flexible tube.
- Hydraulic fluid flows continuously from Ps through the two fixed throttles to the nozzles; through the nozzles to the flapper area and from there to the return connection R. The two fixed throttles and the two throttling points form a hydraulic bridge connection. On the movement of the armature the flapper approaches one nozzle. In this way the hydraulic bridge is unbalanced resulting in a pressure difference at A and B.
Figure D 87: Principle of a flapper-nozzle