Patent ID: 6539726
Filing Date: 2003-04-01
Classification: F17C

Abstract:
A Dewar vessel having an outer casing and an inner vessel with each having openings at their tops connected together by a neck portion forming an evacuable space between the outer casing and the inner vessel and a Dewar opening into the inner vessel, the improvement comprising:an insulative vapor plug held within the neck portion; and a vapor barrier that provides an interference between the plug and the neck portion; wherein the plug and the neck portion are sized so as to define an open space between them that allows a liquid cryogen in a vaporous state to vent from the inner vessel through the Dewar opening; and wherein the interference disrupts migration of the liquid cryogen in the vaporous state out of the Dewar opening through the open space but does not form an air tight seal between the plug and the neck portion.