Nuclear-reactor steam-generator shut-off valve

Claim 1

A fast acting valve for use in the live steam line of a nuclear reactor installation, which steam line leads from a containment to outside thereof, comprising: a. a valve housing having a valve seat with an aperture corresponding to the diameter of the live steam line; b. a valve disc adapted for reciprocal motion with respect to said valve seat to move from a position where it fully closes said aperture to a position where said aperture is fully open providing within the valve a cross section corresponding to the cross section in the live steam line, said valve disc supported for said reciprocal motion on a valve stem; c. a first piston and cylinder arrangement having a piston rigidly coupled to said valve stem, said piston having a range of travel at least equal to the travel of said valve disc between said fully open and fully closed positions; d. a second piston and cylinder arrangement with a range of travel between first and second end positions less than the range between said fully opened and fully closed positions coupled to said stem such as to be moved to said first end position when said valve disc is in the fully closed position and such as to permit moving said valve disc and stem from said closed position to a first intermediate position when at its second end position; e. means coupled to the inlet side of said valve for supplying the steam pressure therein to said first piston and cylinder arrangement when there is a leak in the steam line to move said piston and move said valve disc from a fully open to a fully closed position and thereby move said second piston to its first end position; and f. second means coupled to said inlet and responsive to an excess pressure above normal operating pressure at said inlet to admit steam to said second piston cylinder arrangement to move said piston from said first end position to said second end position thereby opening said valve to said first intermediate position.