Seal assemblies for use with fluid valves are described. An apparatus includes a cage (124), a plug (122) having a seal gland (148) and a seal assembly (300) to be at least partially positioned in the seal gland. The seal assembly includes a back-up ring (302) having a wedge-shaped protrusion (310) and a seal defining a wedge-shaped groove (312) to receive the protrusion. A pressure is to act on the back-up ring to urge the protrusion into the groove. An engagement between the protrusion and the groove is to urge the seal into sealing engagement with an inner surface (126) of the cage.
