Pressure control system

A fluid control system comprising:

• a housing having an inlet passage, an axial bore a portion of which forms an outlet passage, and a chamber;
• a shuttle assembly adapted for movement in the housing to control the flow of fluid from the inlet passage to the outlet passage, the fluid applying a force to a first end of the choke member;
• a source of control fluid connected to the chamber so that the control fluid applies an equal force on the opposite end of the shuttle assembly to control the position of the choke member in the housing in a manner to exert a back pressure on the fluid in the inlet passage;
• the shuttle assembly comprising a shuttle nut disposed proximate the first end for retaining shuttle assembly components,
• the shuttle nut comprising at least two surfaces providing operating fluid pressure area, the at least two surfaces comprising:
• a raised shoulder for engaging a seat member when the shuttle assembly is in a closed position and for providing operating fluid pressure area when the shuttle assembly is in an open position;
• at least one surface for providing operating fluid pressure area when the shuttle assembly is in either the open or closed position;
• wherein the operating fluid pressure area when the shuttle assembly is in the closed position is at least 65 percent of the operating fluid pressure area when the shuttle assembly is in the open position.