The present invention is related to pressure medium powered rotary apparatus units and systems for using the same. The unit is comprising at least two oppositely positioned flange components (2, 6) within an axial distance from each other and connected to each other, an outer casing part between the flange components (2, 6) to connect the said flange components (2, 6), a cylinder room and a piston arrangement. The rotary apparatus unit furthers comprising a channel system arrangement for feeding a pressure medium into the cylinder room and for removing the pressure medium from the cylinder room. An intermediate element (1) substantially having a overall shape of flange is positioned between the flange components (2, 6). The intermediate element (1) comprises at least one curved, elongated groove (1b) penetrating the intermediate element (1) substantially in axial direction, the said groove (1b) forming the cylinder room. The piston arrangement (3c) positioned into the groove (1b) is attached to at least to one flange component (2, 6).