The liquefaction of low boiling point gases, such as air and the components of air, such as oxygen, nitrogen and argon, has been practiced for over 100 years, and the liquefaction of such gases on an industrial scale has been practiced since the beginning of the 20th century. Typically, commercial liquefiers are designed to produce hundreds of tons of liquid cryogens per day. Such industrial liquefiers are reliable, and are capable of producing liquefied gas with relatively high energy efficiency. For consumers of liquefied gas requiring relatively small quantities, small insulated containers, known as dewars, are filled with liquefied gas produced by commercial facilities and transported to the consumer. Consumers of small quantities of liquefied gas include hospitals, which require oxygen for delivery to patients and nitrogen for use as a refrigerant. Also, people suffering from chronic respiratory insufficiency that have been prescribed home oxygen by their physicians may have liquefied oxygen delivered to their residences.
Initially, attempts to provide such a liquefier involved efforts to miniaturize large scale liquefying plants. However, due to the complexity of such systems, which are typically based on the Claude cycle or its variants, these attempts failed. Also, the extremely small mechanical components resulting from the miniaturization of such liquefiers were expensive to produce and unreliable in operation. Current liquefiers often involve complex and/or expensive liquefaction components, and often lack safety features to make a liquefaction system safer for residential, small-scale, and/or portable use.
For the above-stated reasons, it would be advantageous to provide a method and apparatus for improving the safety, efficiency, and/or cost of producing and storing relatively small quantities of liquefied gas at the location where the liquefied gas is to be used, such as at an oxygen therapy patient's residence.