Volume ratio of R718 compressor

The invention relates to the compression of steam in the form of R718 in rotary volumetric machines with or without the addition of an additive in the form of an aqueous solution, in particular for refrigeration, air conditioning and heat pump technologies. The aim of the invention is to prevent as much as possible over-compression or under-compression (which impairs efficiency during operation) by adapting the effective internal volume ratio (so-called iV value) as simply as possible in a positive displacement machine. According to the invention, this is achieved in that, for the rotor profile length LR, the compressor housing (1) has planar, i.e. Flat iV disks (3j) on the length LiV starting from the outlet side (1.2) with a subscript j of 1 < = j < = n, iV disks (3j), where n is the number of iV disks (3j), where n > = 1, each iV disk (3j) having a width bj and comprising a planar surface PF, where n is the number of iV disks (3j), where n is the number of iV disks (3j), where n is the number of iV disks (