Patent ID: 6851658

Claim:
A valve, comprising: a valve body having an inlet port and an outlet port; a valve seat disposed within the valve body defining an opening fluidly communicating between the inlet port and the outlet port; a valve stem extending through the valve body and movable therethrough along an axis; a valve plug coupled to one end of the valve stem, the valve plug having a closed position, in which the valve plug engages the valve seat to form a primary seal, wherein the valve plug is movable away from the closed position to control a fluid flow through the valve seat opening, the valve plug including a conduit adapted to equalize pressure across the valve plug and an annular channel; a sealing ring disposed within the annular channel of the valve plug; and a valve cage disposed within the valve body and having an internal surface sized to receive the valve plug, wherein a gap between the valve cage and the valve plug defines a secondary leak path, the valve cage internal surface including a multi-contoured inner perimeter surface having at least a first perimeter surface and a second perimeter surface, with a first transition surface disposed between the first perimeter surface and second perimeter surface, the second perimeter surface being formed as a generally cylindrical wall substantially concentric with the valve stem axis and being sufficiently proximate the valve plug to sealingly engage the sealing ring, thereby to form a secondary seal restricting fluid leakage through the secondary leak path, and the first perimeter surface being disposed farther away from the valve plug than the second perimeter surface.