Patent Number: 052672751
Section: description

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT The numeral 10 generally designates an apparatus for sealing a joint between a base surface 12 and a sealing device or hollow body 14 having mating end surface 16 with a packing ring or compression gasket means 18. The apparatus 10 is located in a positive pressure environment P.sub.1 such as a boiling water nuclear reactor vessel, and includes a preloading force element 20 for use in response to pressure P.sub.1 against the end 22 of the hollow body 14 opposite its mating end surface 16 and packing ring 18. The apparatus 10 provides a means for establishing, through use of the single element 20, a variable spring preload over the joint area around a leak path 24 to be sealed which will maintain the gasket means 18 under a compressive load sufficient to establish a leak tight or leak limiting joint. As fully taught in U.S. Pat. No. 4,826,217, establishing seals on inclined and/or non-planar surfaces in the bottom of a boiling water nuclear reactor may require a non-uniform or non-symmetric preloading of the sealing gasket 18 over the base surface 12. In FIG. 1, for example, the base surface 12, which is the inside of a boiling water reactor vessel bottom, and the mating end surface 16 are both inclined at an angle (x) to the preload force direction (vertical) for sealing by means of a face seal compression gasket 18. If the application prohibits positive guiding of the hollow body or sealing device 14, it will be necessary to exert a greater percentage of the preload on the downhill side. This is required to limit tendency of the hollow body 14 from slipping downhill and to resist a pressure force (resulting from different uphill and downhill surface areas) that will rotate the sealing device toward the uphill side. The asymmetric preloading force element 20 is a ring of substantial axial depth into which a plurality of circumferentially directed and radially directed through wall slots e.sub.1 to e.sub.3 of varying heights, lengths or angles are machined. The slots can be formed in a stacked pattern and spaced in any variable pattern to achieve an element with the required preload as a function of location. Designing the preloading force element 20 is performed by modeling the element using curved beams loaded normal to the plane of curvature which represents springs in series and series-parallel combinations. By adjusting the size of slots e.sub.1 to e.sub.3 and properly spacing them geometrically and circumferentially, an asymmetric preloading force on the end of hollow body 14 can be obtained in register and alignment with gasket 18. FIG. 3 shows what a typical force schematic drawing showing relative preload force vectors for the apparatus 10 with a spring constant varying from a high to a low value around the circumference of the preloading force element 20, showing the relative asymmetric preloading on the inclined surfaces 12 and 16, and gasket means 18. The left side of FIG. 3 corresponds to the left side of FIGS. 1 and 2. The asymmetric preloading force element 20 of the invention offers several advantages over devices of the prior art such as Belleville washers or springs. Its main advantage is that it offers more flexibility of design in establishing varying spring rates as a function of circumferential location. It also has an improved reliability in that a majority of the intended design preload can be maintained even with through wall failure of a single (or small number of) the slotted elements.