Gas expansion systems have long been known and have found use for many years in cryogenic applications to achieve very low temperatures in spatial regions at or near the expansion volumes thereof. A particularly effective system for such purpose has been described, for example, in U.S. Pat. No. 4,862,694 issued to Crunkleton et al.
Exhaust valves in such cryogenic systems must operate at very low temperatures, e.g., at temperatures in a range from about 5.degree. K. to about 3.degree. K. At such cryogenic temperatures conventional valve structures often tend to provide unsatisfactory and unreliable operation over time. In addition, conventional cryogenic valve structures require complex mechanical operating means that provide heat leak paths to the low temperature region. For example, at such low temperatures, valves requiring metal-to-metal contact between valve elements tend to produce relatively rapid wear and galling of the metal parts thereof. It is desirable to provide an improved exhaust valve structure which operates more reliably at the low temperatures generated at the expansion volumes of a gas expansion system and which is compatible with a low loss cryogenic solenoid operator.