text: Fluid control devices, such as fluid regulators and control valves, are commonly distributed throughout process control systems to control fluid flow rates and/or pressures of various fluids (e.g., liquids, gasses, etc.). For example, fluid regulators are typically used to regulate the pressure of a fluid to a lower and/or substantially constant value. Specifically, a fluid regulator has an inlet that typically receives a supply fluid at a relatively high pressure and provides a relatively lower and/or substantially constant pressure at an outlet. As the high pressure process fluid travels through the process control system, the regulator reduces the pressure of the process fluid at one or more points to supply a process fluid having a lower or reduced pressure to a sub-system or other custody transfer points. For example, a regulator associated with a piece of equipment (e.g., a boiler) may receive a fluid (e.g., gas) having a relatively high and somewhat variable pressure from a fluid distribution source and may regulate the fluid to have a lower, substantially constant pressure suitable for safe, efficient use by the equipment.
  A regulator typically reduces inlet pressure to a lower outlet pressure by restricting fluid flow through an orifice to match the fluctuating downstream demand. To restrict fluid flow between an inlet and an outlet, a regulator typically employs a valve plug to engage a valve seat disposed within the orifice of the regulator body. Some known fluid regulators use a valve seat made from an elastomeric material to provide a tight seal between the valve seat and a valve plug. In such known regulators, the valve seat is typically disposed within the orifice so that the frictional forces between the elastomeric valve seat and the body of the regulator maintain the valve seat within the body of the regulator. However, this known frictional coupling of the valve seat to the body of the regulator may allow the valve seat to shift or move relative the body due to, for example, reverse pressure (i.e., back pressure) conditions, degradation of the elastomeric material, sticking between the valve plug and the valve seat (e.g., due to rubber bloom) when the valve plug moves away from the valve seat, etc. Such shifting or movement of the valve seat relative to the body can cause misalignment between the valve seat and the valve plug, thereby causing unwanted leakage of fluid past the valve seat and affecting the performance of the fluid regulator.