Abstract: A cryogenic refrigerator is disclosed having an expander piston reciprocally mounted within a fluid-tight housing. High pressure gas is supplied to a variable cold volume at one end of the piston through a passageway in the piston when the variable cold volume is at its minimum. Differential forces on the opposite end of the piston cause the piston to move, thereby enlarging the variable cold volume. The expanded cooled gas in the variable volume is vented out through the piston passageway which has been moved into fluid communication with a venting conduit when the variable volume is at its maximum. A heat exchanger operatively disposed between the gas supply and venting conduit allows the cold venting gas to cool the incoming high pressure gas.

Abstract: The Vuilleumier refrigerator cold free piston type displacer operates on pressure pulses generated by relative heating and cooling of gas to raise and lower the pressure in the entire interconnected system. The cold displacer operates with differential areas against which the line pressure acts, and a pneumatic spring to cause reciprocation of the displacer.