| http://www.w3.org/ns/prov#value | - As shown in FIG. 1 to FIG. 3, the gas inlet and outlet valves 30A, 30B used for feeding of the non-oxidizing gas into the clean box 10 have the same structure, in which there are a valve body 32 of a metal such as stainless steel or the like, or a resin, a coil spring 33 as a compression spring, and a filter 34 for removal of dust provided in a cylindrical structure 31 of a metal such as stainless
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