A seal assembly seals first and second operational surfaces spaced apart by a gap. The first surface includes a seal groove having a base surface and first and second side surfaces. A sealing element in the seal groove has a foot portion extending parallel to the base surface which engages the second operational surface. A leg portion extending from the foot portion toward the base surface has first and second surfaces. A back-up ring adjacent to the sealing element prevents extrusion of the sealing element into the gap. A first side of the back-up ring mates with the second surface of the leg portion, and a second side mates with one of the first and second side surfaces of the seal groove. An energizer element located between the base surface and the foot portion applies uniform pressure to the leg and foot portions when the energizer element is compressed.