A device for a machine of displacement type, comprising: a) a non-rotatable housing which surrounds two mutually movable parts ( 101; 102), said parts having co-axial axes of rotation, b) a first part which with its outer circumference is controllably rotationally movable along inside wall of the housing, c) a second part which is controllably movable relative to inner circumferential face of the first part, and having a hub which has at least two radially outwardly directed wings arranged with mutual angular distance, d) at least one inlet aperture and at least one outlet aperture associated with a wall of the housing, characterised in e) that the first part internally has at least two radially inwardly directed wings arranged with mutual angular distance along a curved inside wall of the first part between the wings, f) that portion of the hub between the wings of the second part is in slidable or adjacent contact with a curved, free end portion of the wings on the first part, g) that a curved, free end portion of each wing on the second part is in slidable or adjacent contact with the curved inside wall on the first part which is located between respective ones of two neighbouring of said wings on the first part, h) that the first part and the second part are both continuously rotatable movable, but with mutually variable movement, the wings of the second part being movable between respective neighbouring wings on the first part, so that chambers ( 159 - 162) which are created between co-operative pairs of wings (139; 147) on the first part and the second part successively increase and decrease, and decrease and increase, respectively, in volume during the course of a rotation cycle of the created chambers, i) that one first axial end of the two parts ( 102; 101) is in slidable or adjacent contact with a first cover ( 104; 105; 106) having apertures ( 128; 129) for controlled communication with the chambers ( 159 - 162), the first cover ( 104; 105; 106) constituting said wall, and that a second axial end of the two parts ( 102; 101) is covered by a second cover which is attached to the first part and rotary therewith, and the second part being in slidable or adjacent contact with the second cover, and j) that movements of said mutually movable parts ( 102; 101) are caused by a controlling gear arrangement which operationally co-operates with a rotatable main drive shaft of the machine. a) a non-rotatable housing which surrounds two mutually movable parts ( 101; 102), said parts having co-axial axes of rotation, b) a first part which with its outer circumference is controllably rotationally movable along inside wall of the housing, c) a second part which is controllably movable relative to inner circumferential face of the first part, and having a hub which has at least two radially outwardly directed wings arranged with mutual angular distance, d) at least one inlet aperture and at least one outlet aperture associated with a wall of the housing, e) that the first part internally has at least two radially inwardly directed wings arranged with mutual angular distance along a curved inside wall of the first part between the wings, f) that portion of the hub between the wings of the second part is in slidable or adjacent contact with a curved, free end portion of the wings on the first part, g) that a curved, free end portion of each wing on the second part is in slidable or adjacent contact with the curved inside wall on the first part which is located between respective ones of two neighbouring of said wings on the first part, h) that the first part and the second part are both continuously rotatable movable, but with mutually variable movement, the wings of the second part being movable between respective neighbouring wings on the first part, so that chambers ( 159 - 162) which are created between co-operative pairs of wings (139; 147) on the first part and the second part successively increase and decrease, and decrease and increase, respectively, in volume during the course of a rotation cycle of the created chambers, i) that one first axial end of the two parts ( 102; 101) is in slidable or adjacent contact with a first cover ( 104; 105; 106) having apertures ( 128; 129) for controlled communication with the chambers ( 159 - 162), the first cover ( 104; 105; 106) constituting said wall, and that a second axial end of the two parts ( 102; 101) is covered by a second cover which is attached to the first part and rotary therewith, and the second part being in slidable or adjacent contact with the second cover, and j) that movements of said mutually movable parts ( 102; 101) are caused by a controlling gear arrangement which operationally co-operates with a rotatable main drive shaft of the machine.