A radially sealed centrifugal pump comprises a casing (2) to which a shaft (4) is rotatably connected, and an impeller (5), connected to said shaft (4), free to rotate within said casing (2), and said pump has, between said casing (2) and said impeller (5) which are in relative motion, opposed surfaces (21, 22) which are substantially perpendicular to the axis of said impeller (5) and which form the seal.