Re-energizable valve and valve seats

Disclosed is a type of valve of the sort that controls the flow of fluid and that contain a plug and at least one seat against which the plug presses to close the valve. The novel valve has floating seats, which can seal downstream, and only when desired, can also be re-energized to seal upstream. The upstream sealing capability of the invention provides a backup against downstream leaks, such as from low-pressure flows or parts failures such as due to wear or breakage. The valve can seal upstream through the use of hydraulic fluid, which is injected at high pressure into a sealed cavity behind the upstream seat, thereby forcing the seat against the plug. A novel seat seal design permits sealing against the fluid flow as well as isolation of the hydraulic injection ports from the fluid flow, during all operating states of the valve.