Abstract: A rotor (18) is disposed in a bore (14) of a cylinder (13) and carries vanes (33), (34), (36), (37) in radial slots (28), (29), (31), (32), the vanes (33), (34),(36), (37) being urged into engagement with the wall of the bore (14) by oil pressure applied to inner ends of the vanes (33), (34), (36), (37). The cylinder (13), rotor (18) and vanes (33), (34), (36), (37) are configured to displace refrigerant fluid or the like through the bore (14) from an inlet (19), (21) to an outlet (22), (23) upon rotation of the rotor (18). The trailing outer edges (28a') of the slots (28), (29), (31), (32) are chamfered, thus reducing frictional resistance between the vanes (33), ( 34), (36), (37) and slots (28), (29), (31), (32) to radial movement and producing a reservoir (28c') for oil forced through clearances between the slots (28), (29), (31), (32) and vanes (33), (34), (36), (37).