A compact spring-loading design has been proposed to increase the reliability of seals in the joints of vacuum cryogenic systems. Heretofore, such joints have been, variously, compact or reliable, but not both, for the following reasons: In all such joints, sealing is effected by compression of soft metal (typically, indium or alloys of indium) O rings between flanges. Over time, the soft O-ring metal flows, with consequent reduction of preload, sometimes leading to loss of seal. To ensure reliable seals, it is necessary to spring-load the flanges to maintain compression of the O rings. However, spring-loaded joints of traditional design are not compact.

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The Outer Portion of One of the Flanges would be cut to form leaf springs, which would be used for spring loading of the O ring.
The proposed compact spring-loading design is related to a prior non -compact design in which (1) one of the flanges of a joint is cut so that it acts somewhat like a leaf spring and (2) the bolt-circle diameter of the flange is made considerably greater than the major diameter of the O ring so that the flange can bend elastically and its deflection is spread out over the annulus between the O ring and the bolt circle. In the pro- posed design, leaf springs with a thickness less than that of the flange would be formed in the bolt-circle region by cutting a combination of meridional (radial-axial) and annular slots in the flange, as shown in the figure. This design would afford the elasticity needed for spring loading, without need to make the bolt circle much larger than the O ring.

This work was done by Bob Bamford, Talso Chui, and Warren Holmes of Caltech for NASA’s Jet Propulsion Laboratory.