Servo booster mechanism

A servo booster mechanism (18) having a piston (48) responsive to movement of a plunger (84) by an input signal for controlling the rate of fluid flow past a seat (82) into a passage (80) for distribution to the surrounding environment. A first restrictor (75) creates a first pressure drop in a supply fluid pressure Ps to present an operational chamber (46) with fluid at a pressure Px. A second restrictor (openings 74-76) creates a second pressure drop in fluid pressure Px supplied from the operational chamber (46) to present control chamber (88) with fluid at a pressure Ph. The difference in pressures combine to act on the piston (48) and plunger (84) to provide a constant force at stem (26), which provides a feedback to the input member (12), and provide a linkage (22) with a force to hold a position sensor (24) in a stationary position.