When the pressure of the air acting on feedback bellows 1 is increased, the bellows is compressed, turning lever 2 about fixed axis A. Lever 2 turns link 3 from which shutter 4 is suspended. As a result, shutter 4 approaches nozzle 5. When the air pressure drops, the elements of the direct feedback mechanism operate in the reverse direction.
$3910$LHP,Rg$