Patent Number: 047160055
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will be described as applied to a pressure vessel in a nuclear reactor, however, it will be realized by those skilled in the art that it has wider application to a great many installations where it is desired to form a pressure tight seal between two planar sealing surfaces. Thus, by way of examples which are not meant to be limiting, the invention could also be utilized to provide a pressure tight seal for pump housings, fluid conduits and other types of pressure vessels. As illustrated in FIG. 1, the nuclear reactor pressure vessel 1 in connection with which the invention will be described, includes an upright cylindrical body 3 having a radially, outwardly extending flange 5 at its upper end which defines an axially facing planar sealing surface 7. A removable, hemispherical head 9 terminates at its lower end in a mating, radially extending flange 11 which also defines an axially facing sealing surface 13. The head 9 is secured to the pressure vessel body 3 by a number of bolts 15 which extend through bores 17 and 19 in flanges 5 and 11 respectively. Under normal operating conditions, reactor coolant is introduced into the pressure vessel 1 at a pressure between 2000 and 3000 psi. In accordance with the invention, a seal assembly 21 provides a pressure tight seal between the confronting sealing surfaces 7 and 13 on the flanges 5 and 11. As can best be seen from FIGS. 2 and 3, the seal assembly 21 includes a spacer unit 23 and a toroidal, crushable seal member 25. The spacer unit 23 includes a flat, ring shaped member 27 with a resilient inner portion which is formed by a circular coil spring 29 seated in a radially extending V-shaped recess 31 in the inner surface formed by the bore 33 of the ring shaped member. Alternatively, an elastomeric solid or hollow O-ring can be used in place of the circular coil spring 29. The toroidal, crushable seal member 25 is a circular metallic tube which is received in the bore 33 in the ring shaped member 27 and rests on a shoulder 35. The seal member 25 is locked in place within the ring-shaped member 27 by the circular coil spring 29 so that the seal assembly 21 can be maneuvered as a unit. This greatly facilitates alignment of the seal and is an important feature of the invention. The ring-shaped member 27 is provided with a number of axial bores 37 which register with the flange bores 17 and 19 to positively locate the seal assembly 21 between the sealing surfaces 7 and 13. The thickness t.sub.1 of the seal member 25 is greater than the thickness t.sub.2 of the ring-shaped member 27, so that as the bolts 15 are tightened to draw the sealing surfaces 7 and 13 toward each other the seal member 25 is contacted first and crushed betwen the sealing surfaces. As this occurs, the seal member 25 flattens out against the sealing surfaces 7 and 13 as shown in FIG. 4 to form an in depth seal. The spacer unit 23 maintains the proper position of the seal member 25 while it is being crushed yet the resiliency of the circular coil spring 29 permits it to expand radially as it is deformed. Preferably, the ring-shaped member 27 is made of a rigid material such as steel so that its thickness, t.sub.2, provides a positive limit for the crushing of the seal member 25. The tubular seal member 25 is provided with radial bores 39 along its inner surface to admit pressurized reactor coolant into the interior of the seal member to improve its sealing capability. The alignment of the toroidal seal member 25 relative to the planar sealing surfaces 7 and 13 without the necessity of cutting grooves in, or providing other special arrangements on the planar sealing surfaces, is another important feature of the invention. By way of example, a typical seal unit made in accordance with the teachings of the invention for use in sealing the head on a nuclear reactor pressure vessel includes an annular 160.822 inch O.D. seal member 25, made of 0.5 inch O.D. tubular stainless steel material with a 0.050 inch wall thickness and 0.06 to 0.07 inch apertures 39 and coated with a 0.001 to 0.002 layer of silver to fill in machining imperfections. The spacer unit 23 includes a flat 0.473 inch thick ring member 27 having a 184 inch O.D. and a 160.54 inch I.D., and a solid annular 161.35 inch O.D. resilient member 29 made of 0.25 inch elastomeric material. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.