Babban ka'idar rabuwar iska shine amfani da gyaran gyare-gyare na cryogenic don tara iska cikin ruwa da kuma raba iska bisa ga yawan zafin jiki na kowane bangare. Hasumiyar gyara matakai biyu a lokaci guda tana samun tsantsar nitrogen da iskar oxygen a sama da kasan hasumiya ta sama. Hakanan yana yiwuwa a fitar da iskar oxygen da ruwa nitrogen daga gefen evaporation da gefen natsuwa na babban sanyaya bi da bi. Rabuwar iska a cikin hasumiya mai gyara ya kasu kashi biyu, an raba iska a karon farko a cikin hasumiya ta ƙasa don samun ruwa nitrogen kuma a lokaci guda samun iskar ruwa mai wadatar oxygen. Ana aika iskar ruwa mai wadataccen iskar oxygen zuwa hasumiya ta sama don gyarawa don samun iskar oxygen da tsantsar nitrogen. Hasumiya ta sama ta kasu kashi biyu: tare da shigar ruwa-iska a matsayin iyaka, babban sashi shine sashin gyarawa, wanda ke gyara iskar gas mai tasowa, mai dawo da sashin oxygen, kuma yana tsarkake tsarkakewar nitrogen, kuma sashin ƙasa shine sashin tsiri don cire abubuwan nitrogen a cikin ruwa, an raba shi don haɓaka iskar oxygen na ruwa.