Feedback of the position of the control spool of a continuously adjustable valve by centring the control spool with spring action (item 8 and 9 (Figure B 3)).
Figure B 3: Barometric feedback: 1 = Torque motor; 2 = Flapper-nozzle system; 3 = Spool; 4 = Spring; 5 = Baffle plate; 6 = Nozzle; 7 = Spool sleeve; 8 and 9 = Pressure chambers for the pilot stage