A bearing arrangement for a unit that is mutually turnable around a centre of rotation (R) comprising an external part (1) and an internal part (7), which, with the aid of high hydraulically acting pressure, is arranged to achieve a reciprocating rotary motion, or that is arranged to achieve a high hydraulic pressure from an applied torque from a reciprocating motion, whereby the external part (1) is provided with side walls arranged to axially surround at least a part of the internal part (7), and whereby the external part (1) comprises a radially inwardly arranged and essentially surrounding cavity (11, 12, 13, 14) in which the internal part (7) is arranged such that it can be rotated, which cavity (11, 12, 13, 14) is limited in the circumferential direction by at least one wing (3, 4) that protrudes inwards from the external part (1) and also limited by at least one wing (9, 10) that protrudes radially outwards from the internal part (7), which wings (3, 4, 9, 10) limit at least two chambers or compartments (11, 12, 13, 14) between the external part (1) and the internal part (7). At least one of the side walls of the external part is fixed connected with the, at least one, wing (3, 4) that protrudes radially inwards towards the internal part (7), which wing demonstrates a surface that faces radially inwards and that has a circular concave curvature for connection with an outwardly facing circular convex contact surface (8) at the internal part (7).