The interior of a rotating body 62 having the shape of a hollow flywheel is made up of a cascade sequence of basins 14 located along a spiral path, formed and perforated 12 likewise the "Nautilus" shell interior; a pressure fluid source 30 feeds the fluid under pressure which is to press on the blades of the spiral; said fluid being linked to a compressor 30,38 which is controlled by the instantaneous pressure. A discharge passage located at the centre of the flywheel 62 and controlled by a shutter, 85 either permits or prevents the fluid escape, a succession of pressures and vacuums and hence a torque being set up by the opening of said passage.