A gas replacement method for an expander of a cryocooler, the expander including an expander cylinder, a pressure switching valve that switches a pressure inside the expander cylinder, a connection flow path from the pressure switching valve to the expander cylinder, and an expander motor that drives the pressure switching valve, includes connecting a nonflammable gas source to the connection flow path or the expander cylinder, and purging a residual gas in the expander cylinder with a nonflammable gas from the nonflammable gas source while the expander motor is stopped.

A rotary valve mechanism includes a stator valve member furnished with one of either a dome-shaped high-pressure recess area made of a polymer or a high-pressure flow path made of metal, and a rotor valve member furnished with the other of either the dome-shaped high-pressure recess area made of a polymer or the high-pressure flow path made of metal, and seals a high-pressure region being the high-pressure flow path communicated with the dome-shaped high-pressure recess area and is disposed adjoining the stator valve member such as to isolate the high-pressure region from its low-pressure surrounding environs.

A connecting device in a pulse tube cooler system branches such that a first line branch (11) has a first flexible line segment (4a) and a second line branch (12) has a second flexible line segment (4b), the flexible line segments being arranged in parallel with and offset from one another. The flexible line segments each have a front segment end (17, 18) and a rear segment end (19, 20), the front segment end (17) of the first flexible line segment (4a) and the rear segment end (20) of the second flexible line segment (4b) are rigidly connected to one another, the rear segment end (19) of the first flexible line segment (4a) and the front segment end (18) of the second flexible line segment (4b) are rigidly connected to one another, and there is no continuous rigid connection between the control valve and the cold head.