Patent ID: 8650887

Claim:
A method of holding a cryogenic fluid comprising liquefied gas and vapor in a thermally insulated cryogen space defined by a storage tank, wherein said cryogen space is partitioned so that it is divided into a main storage space and an auxiliary space, said method comprising: (a) establishing a vapor-filled ullage space when said main storage space is being vented and re-filled with said cryogenic fluid, by draining said liquefied gas from said auxiliary space to said main storage space through a first fluid passage provided through said partition, wherein said first fluid passage is sized to allow said liquefied gas to flow there through under the influence of a vapor pressure differential permitted by said partition, said liquefied gas draining at a rate that allows said auxiliary space to be drained of said liquefied gas to establish said vapor-filled ullage space with a liquefied gas volume that is at least as large as a predetermined ullage volume in less than the time needed to vent and re-fill said main storage space with said cryogenic fluid; (b) preserving said vapor-filled ullage space by restricting a flow of said liquefied gas through said first fluid passage from said main storage space into said auxiliary space when said cryogen space is being re-filled with said cryogenic fluid, wherein said flow of liquefied gas through said first fluid passage is restricted by regulating said flow of liquefied gas with a valve that comprises a valve member that is actuatable between an open and a seated position by fluid forces within said cryogen space, whereby the flow of liquefied gas is restricted by said valve when said valve member is in said seated position; (c) restricting said cryogenic fluid flow through a second fluid passage provided through said partition, so that said vapor pressure differential can develop across said partition when said main storage space is being vented and re-filled with said cryogenic fluid, and whereby a detectable back pressure occurs when said main storage space is filled with said cryogenic fluid when said cryogenic fluid is being introduced into said main storage space; and (d) detecting when said storage tank is full and stopping re-filling when said storage tank is full; further comprising regulating a second fluid flow through said second fluid passage with a second valve comprising a second valve member that is actuatable by other fluid forces within said cryogen space, whereby said second valve opens to allow said cryogenic fluid to flow from said main storage space to said auxiliary space when vapor pressure in said main storage space is higher than vapor pressure within said auxiliary space by a predetermined amount.