Abstract: A low-temperature end of a pulse tube (1) and a low-temperature end of a cold accumulator (2) are communicated with each other through an endothermic connection passage (3), so that refrigerant gas to be supplied from a compressor (7) to a high-temperature end of the cold accumulator (2) through a refrigerant gas passage (28) is introduced from the low-temperature end of the pulse tube (1) to the high-temperature end thereof through the cold accumulator (2) and the endothermic connection passage (3). A buffer tank (30) is connected to the high-temperature end of the pulse tube (1) through a first orifice (31). A sub gas passage (32) branched off from the refrigerant gas passage (28) is connected to the the buffer tank (30) through a second orifice (33).

Abstract: Two three-way valves (12) (13) of the rotary type are arranged in parallel in a high-pressure refrigerant gas passage (15) of a compressor (7). A high-temperature end portion of a cold accumulator (2) is communicated with one three-way valve (12) of the rotary type through a main gas passage (19) as well as a high-temperature end of a pulse tube (1) is communicated with the other three-way valve (13) of the rotary type through a sub gas passage (20). A low-pressure port of each three-way valve (12)(13) is communicated with a low-pressure refrigerant gas return passage (17) of the compressor (7) respectively. A flow regulating member (21) is interposed in the sub gas passage (20). Both the three-way valves (12) (13) are synchronously rotated. A valve opening-closing timing of the one three-way valve (12) or (13) is adjustably changed relative to that of the other three-way valve (13) or (12).

Abstract: In an apparatus for producing liquid nitrogen by supplying to a nitrogen gas separated from the atmosphere and then purified by an air separating device (4) into an insulated container (1) equipped with an extremely low temperature refrigerator, there are provided a pressure sensor (21) for detecting a pressure within a product vessel (20) of the air separating device (4) and a negative pressure sensor (16) for detecting a negative pressure within the insulated vessel (1) respectively. When at least one of both sensors (21) (16) detects a freezing of an impurity gas contained in the supplied nitrogen gas by reaching a predetermined pressure, an operation of the extremely low temperature refrigerator is stopped depending on the detection by one of both the sensors.