Cryogenic fluid transfer joint employing a stepped bayonet relative-motion gap

In cryogenic apparatus including a rotor wherein the interior portion thereof is bathed in liquefied coolant at cryogenic temperatures, a joint for supplying said liquefied coolant to a conduit within said rotor rotating in unison with said rotor, said joint comprising:

• a hollow shaft coupled to said rotor so as to be rotatable therewith, said conduit extending from said rotor into the hollow interior of said shaft;
• stationary bayonet means having an outlet penetrating into the interior of said conduit and delivering said liquefied coolant from said outlet into the interior of said conduit, said liquefied coolant within said conduit being centrifugally forced against the interior surface of said conduit;
• and
• annular means rigidly coupled to the wall of said conduit and rotatable in unison therewith, said annular means being disposed concentrically about, and spaced apart from, said bayonet means so as to define a relative-motion gap therewith, said relative-motion gap having a smaller outer diameter than the inner diameter of the liquefied coolant centrifugally forced against the interior surface of said conduit and thereby admitting a flow of gasified coolant from the interior of said conduit in a direction opposite to the flow of said liquefied coolant through said bayonet means so as to help cool said bayonet means while precluding entry of liquefied coolant into said gap from the interior surface of said conduit.