Design and performance of a 30 l h helium liquefier/refrigerator with plastic piston expansion engines

An all-welded, simplified expansion engine with plastic piston and plastic piston rings was designed and tested. With expansion engines of this type, a helium liquefier/refrigerator of 30 l h⁻¹ capacity was built and its design, performance and controls are described. The liquefaction cycle is a Claude cycle with the helium gas being purified by a low temperature purification circuit added inside the liquefier.This liquefier produced about 30 000 litres of liquid helium during the last twelve months.