Gas replacement method for expander of cryocooler, cryocooler, and gas replacement pipe

Abstract

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.

What is claimed is: 
     
         1 . 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, the gas replacement method comprising:
 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.   
     
     
         2 . The gas replacement method according to  claim 1 ,
 wherein the connecting includes connecting the nonflammable gas source to a gas receiving port of the connection flow path via a gas replacement pipe, and   the purging includes supplying the nonflammable gas from the nonflammable gas source to the expander cylinder from the gas replacement pipe through the gas receiving port and exhausting the residual gas from a gas outlet port of the gas replacement pipe or of the expander.   
     
     
         3 . The gas replacement method according to  claim 2 ,
 wherein the expander includes a high pressure port and a low pressure port connected to the expander cylinder via the pressure switching valve, and   the purging includes supplying the nonflammable gas to the expander from the high pressure port and the low pressure port.   
     
     
         4 . The gas replacement method according to  claim 1 ,
 wherein the nonflammable gas is a working gas of the cryocooler.   
     
     
         5 . A cryocooler comprising:
 an expander cylinder;   a pressure switching valve that switches a pressure inside the expander cylinder;   a high pressure port and a low pressure port connected to the expander cylinder via the pressure switching valve;   a connection flow path from the pressure switching valve to the expander cylinder; and   a gas receiving port that is different from the high pressure port and the low pressure port and is connected to the connection flow path to allow a gas to flow into the connection flow path.   
     
     
         6 . The cryocooler according to  claim 5 , further comprising:
 an expander housing that is coupled to the expander cylinder and accommodates the pressure switching valve,   wherein the gas receiving port is provided in the expander housing.   
     
     
         7 . The cryocooler according to  claim 6 ,
 wherein a gas outlet port is provided in the expander housing in addition to the high pressure port, the low pressure port, and the gas receiving port.   
     
     
         8 . The cryocooler according to  claim 5 ,
 wherein the gas receiving port has a size different from sizes of the high pressure port and the low pressure port.   
     
     
         9 . The cryocooler according to  claim 5 ,
 wherein a flow path cross-sectional area of the gas receiving port is smaller than a flow path cross-sectional area of the connection flow path.   
     
     
         10 . A gas replacement pipe used for gas replacement of an expander of a cryocooler, the gas replacement pipe comprising:
 a main pipe that is connectable to a nonflammable gas source;   a first branch pipe that branches from the main pipe and is connectable to a gas receiving port of the expander;   a second branch pipe that branches from the main pipe and is connectable to a high pressure port of the expander; and   a third branch pipe that branches from the main pipe and is connectable to a low pressure port of the expander.