Improvement of low-temperature piston ring

A piston ring set of a cryopump includes a first piston ring and a second piston ring that are differently shaped and cooperatively shaped to form a hollow cylindrical shape when abutting each other. The first piston ring is C-shaped and defines an intermediate portion disposed between the first end portion and the second end portion. A piston ring gap is disposed between a first distal end of the first end portion and a second distal end of the second end portion. When the first piston ring abuts the second piston ring to form a hollow cylindrical shape, the second piston ring does not extend along a middle portion of the first piston ring, and the second piston ring extends along a first end portion and a second end portion of the first piston ring. 一种低温泵的活塞环组，包括第一活塞环和第二活塞环，所述第一活塞环和第二活塞环不同地成形并且当彼此邻接时协作地成形以形成中空的圆柱形形状。第一活塞环是C形的，并限定了设置在第一端部部分和第二端部部分之间的中间部分。活塞环间隙设置在第一端部部分的第一远端和第二端部部分的第二远端之间。当第一活塞环与第二活塞环邻接从而形成中空圆柱形形状时，第二活塞环不沿着第一活塞环的中间部分延伸，而第二活塞环沿着第一活塞环的第一端部部分和第二端部部分延伸。