Gas energized seal for Gifford-McMahon expander

A Gifford-McMahon (GM) expander with improved seal characteristics, the GM expander comprising:

• a displacer having a groove on the outer circumference (Rd), wherein the groove is defined by an upper surface, a lower surface and a side surface connecting said upper and lower surfaces;
• a cylinder having an inner surface (Rc), wherein said displacer axially reciprocates in the cylinder;
• a seal ring placed in said groove, wherein the seal ring has an axial length along an axial direction of the displacer;
• a cold displaced volume in the cylinder at a lower end of said displacer;
• a warm displaced volume in the cylinder at an upper end of said displacer;
• and
• a regenerator between said cold and warm displaced volumes;
• wherein said seal ring has an outer surface (Rro) adjacent to said cylinder and an inner surface (Rri) adjacent to said side surface of the groove, and wherein a first radial gap (W1) is formed between said inner surface of the seal ring and said side surface of the groove and a second axial gap (W2) is formed by a difference between the axial length of said seal ring (Lr) and a distance between said upper and lower surfaces (Lg) of the groove, wherein the second axial gap (W2) is greater than the first radial gap (W1).