G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
G05D16/00—Control of fluid pressure
G05D16/04—Control of fluid pressure without auxiliary power
G05D16/10—Control of fluid pressure without auxiliary power the sensing element being a piston or plunger
G05D16/109—Control of fluid pressure without auxiliary power the sensing element being a piston or plunger with two or more pistons acting as a single pressure controller that move together over range of motion during normal operations