Abstract
The improvement of reliability of the cryogenic system is now an indispensable requisite. it is no exaggeration to say that the cryogenic refrigerator is especially lagging behind the superconductivity devices in reliability.
This report describes what ideas are necessary to achieve a reliable cryogenic system design. These ideas were applied to the development of a small-sized helium refrigerator, particularly of its expansion engine.
As a result, we have succeeded in developing an automatic valve expansion engine, which provides a mean time between failures (MTBF) of 5, 000hrs at 70% confidence level.
