Co-axial double-inlet valve for pulse tube cryocooler

A Gifford-McMahon (GM) type double-inlet pulse tube system providing cooling at cryogenic temperatures, comprising;

• a compressor supplying gas at a supply pressure through a supply line and receiving gas at a return pressure through a return line;
• a valve assembly connected to the supply and return lines;
• a pulse tube cold head connected to the valve assembly, wherein the valve assembly cycles gas between the supply pressure and the return pressure to the pulse tube cold head through a connecting line, the pulse tube cold head comprising:
• a regenerator having a warm end and a cold end;
• a pulse tube having a warm end and a cold end;
• a co-axial double-inlet valve comprising:
• a base having an adjustable port, wherein the base is configured to be adjustable along an axial direction;
• a fixed needle partially engaged in one end of the adjustable port;
• an adjustable needle partially engaged in another end of said adjustable port, wherein the adjustable needle is arranged co-axially with the fixed needle;
• and
• a body for housing the base, the fixed needle and the adjustable needle;
• a first line extending from the connecting line to the warm end of the regenerator, wherein the co-axial double-inlet valve is connected to the first line;
• a second line connecting the cold end of the regenerator to the cold end of the pulse tube;
• a third line extending from the warm end of the pulse tube to a buffer volume through a single-inlet valve;
• and
• a fourth line extending from the co-axial double-inlet valve to the warm end of the pulse tube.